Spreadsheets
Efficiency: high , Difficulty: medium , Time: high , Annoying others: none
It is a good idea to take notes about how big kingdoms are. Check them numerous times/day. If they increase much in land, they might be good landgrabs. If they don’t increase much in NW and have the same amount of land for a while, they might be good banks. If you find a kingdom which isn’t open but would be a good landgrab if he was, send a message to yourself with his stats, kingdom name, sector, NW, and land. Check the kingdom often - soon or later, he will most likely make a big attack, and then you will know when to hit him. There is also a spreadsheet in the menu to the left, which can be used for bank- or target finding by comparing sector growth.

Copycat attacking
Efficiency: medium , Difficulty: low , Time: low , Annoying others: very high
If you have one or several sectormates of about your size, let them do all the hard work, ask thm about the SoM's and hit the same kingdoms as they hit after them. You will only get 90% as much land as them, and some people will be very upset if they get hit multiple times by people from the same sector, but sometimes it might be worth it. Especially if you don't have time to look around for targets, or can't afford using probes for the moment.

Husgalz insane mining strategy
Efficiency: high , Difficulty: high, Time: high, Annoying others: low
in order to use this strategy, you have to already be so big that no one can grab you safely. Then you make so much offense that you can hit other people if you need to, so they will feel threatened. After that, start spending allyour money on exploring, and construct star mines on the new land. Always make sure that no one is able to grab you, and you can probably finish really good, even if your army is really bad.

Powerless Mountainous
Efficiency: medium , Difficulty: medium , Time: medium , Annoying others: low
Being powerless will give you -20% to offense and defense, -20% to population, and -90% to civilian birth rate. Therefore, you should always try to have enough power plants to have a positive power income, unless you are using this strategy. If you are powerless on purpose, you don’t use any power plants at all, but use that land for other buildings. When attacking someone, you first hit a small kingdom with one war leader to gain power (then you won’t be powerless until the hour changes), and then use the other three WL’s to attack a bigger kingdom after you’ve got power.

Anti-targeting suicide
Efficiency: medium , Difficulty: high, Time: very high , Annoying others: very high
Suiciding is to send out most of your army to hit someone. If you are getting targeted, but not too many kingdoms are attacking you, you can sometimes suicide on purpose and get beat down to tiny size. If your WL's return with your army before you are completely dead, many kingdoms will stop attacking you, because very few people would send over 10k tanks for 10 land. However, it will be very hard staying alive afterwards, since you won't have enough support for your military on your remaining land.

Depressland’s residenceless+barracksless strategy
Efficiency: low , Difficulty: very high, Time: very high, Annoying others: high
With this strategy, you raze all your residences and barracks a short while into the game. Your population will then leave you, but if you are very active you might be able to kidnap population from other kingdoms (which gives you 1/4 of the civilians which you manage to kidnap) to keep enough population to not die, and still get a lot of extra land to use for other buildings.
In SK 2.0, the population losses are increased a lot when being residenceless, so do this on your own risk. Two or three other players can easily kill you with probings while you are sleeping if you have no residences, and if the server crashes for half a day, you are dead... so it is not a recommended strategy, even if it used to be great with the old game rules.

Residenceless, powerless and barracksless combo
Efficiency: low, Difficulty: very high , Time: very high, Annoying others: high
You combine the two strategies above. Both residenceless, barracksless and powerless means a lot of extra land for Star Mines.

Immediately residenceless and powerless
Efficiency: none , Difficulty: very high, Time: very high, Annoying others: very high
With this strategy, you raze your barracks, residences and/or powerplants while still in newbie mode. Probably the most stupid strategy you can use, but I have seen people do it. Don’t try this unless you want your kingdom to die.

Probing
Efficiency: high, Difficulty: medium , Time: medium , Annoying others: very low
Never underestimate the power of probes. The more of them you have, the better. Try to always shield them, if possible. Also don’t probe people if you know that you will be unsuccessful. It is really important to have many probes early (not immediately after leaving newbie mode, but a few days later).
With a high probe ratio, you will be less likely to fail and therefore lose less probes, and keep the high probe ratio for most of the game. With a low ratio, you will lose more, and end up in an evil loop where your probe ratio becomes worse all the time, making you fail even more, and failed probings are of no use at all. The more probes you have, the harder it is also going to be for other players to probe you, and most people will never hit you if they can't get your stats.

1 probe trick / No factories
Efficiency: medium , Difficulty: high , Time: medium , Annoying others: high
You can try to send 1, 2 or 3 shielded probes when probing someone, and you will probably be successful about 5 % of the times. This little cheat only works when you want to find out their kingdom stats, research stats, military stats or building stats, and is quite useless when robbing, arsoning or kidnapping from someone, since you will only get messages like "Our intelligence reports that your probes have kidnapped 0 civilians. Unfortunately, we lost 1 probes on this mission." then. People which play without factories usually rely on stats which friends get for them, or which are posted in forums. If you are planning to play very active, this strategy is quite useless, but a low amount of factories can be a nice combination when mixed with the turtling strategy, since many probes are not needed then.

Omni's high-population F&W exploration strategy
Efficiency: very high , Difficulty: high, Time: low, Annoying others: medium
As Forest and Wilderness, you can make a lot of money if you base all your income on residences and civilians. With this strategy, you play as that planet type, keep residences on 60% of your land or more, explore max. land all the time, and draft a lot of laser troopers (laser dragoons instead when it is researched). You keep exploring until you have approximately 8-10k land, have quite a weak offensive force, but always have enough LT's or LD's to make it impossible for people to hit you without suiciding. After this, you will probably be able to train 30-40k dragoons/day, and can soon start making big attacks.

FTB's residenceless supersoldier F&W strategy
Efficiency: high, Difficulty: very high, Time: high, Annoying others: medium
This strategy has been used successfully by Fade to Black and numerous other elite players. You play as Forest and Wilderness and put a lot of land into residences early on. You can then train huge amounts of soldiers. Keep doing so for a few weeks, even if you can't draft more than a small part of them into stronger military units. FTB had 1.5 million soldiers at one point of the game. After this, it is time to raze all the reisdences and barracks, and construct huge amounts of star mines on your land. Your income will be low for a while, but after that, it will become so high that you can draft hundreds of thousands of soldiers into tanks every day, if you are just big enough. Since you already have big amounts of soldiers, you will only need to keep enough population to stay alive, which means one or a few kidnappings/day on players with high population, or disbanding of a few soldiers every few hours.

Superturtling
Efficiency: high , Difficulty: low, Time: very low, Annoying others: medium
You only get enough offense to attack inactives or suiciders and live on those, while getting a strong defense, having many probes (which you rob people with - since you don't need to waste probings on stats, you can rob a lot) and exploring your land. Turtling kingdoms usually have a strong defense and a really weak offense, and they rarely get hit.

Counterbashing
Efficiency: medium , Difficulty: high, Time: high, Annoying others: high
When you have a big, tank-based army, you suicide, but leave enough defense at home to not get killed completely. You will then lose your land, and have to stay alive on kidnappings. However, you will still have a strong army, so you will be able to counter-strike bashers, and since you will have a little land left, not many persons will try to attack you.

No training camps
Efficiency: medium , Difficulty: low , Time: none , Annoying others: none
If you spend a lot of money on exploring/building, or use to buy cheaper military units, such as troopers, laser troopers, laser dragoons and dragoons, it might be better if you don’t use any training camps, but use that land for other buildings instead. It works well as long as you’re not an all-tank player.

Low research strategy
Efficiency: medium , Difficulty: medium , Time: none , Annoying others: none
For big players, it is usually an impossibility to keep all the land-based bonuses maxed later on in the game, since that would require a huge amount of scientists. Therefore, many people decide to give specific researches higher priority, or to not care about some of the researches at all. Most big players only try to keep their military and money bonuses maxed as most, since those two are the most important ones, and several people in top 100 play completely without population research and power research (which only makes them require a little bit more powerplants and residences than other players). Frequency Decryption and Warp Core are ways too expensive compared to how useful they are, so they are usually not needed at all, unless you have an excess of scientists and all the other researches already maxed.

End game NW boost with Star Mines
Efficiency: high , Difficulty: medium , Time: none, Annoying others: none
Most top players raze their probe factories, (and also powerplants and air support bays in some cases) when it is 5-20 days left until the end of the game, and construct Star Mines on all the free land, increasing their income a lot. This also works for smaller players if they just have a good amount of probes saved up since earlier.

Omni's Ultimate Strategy
Efficiency: none (was superior before), Difficulty: medium , Time: none, Annoying others: none
This strategy is the only one known so far which allowed exponential kingdom growth. However, BCart has now changed the population loss formula, which makes it impossible to use it any more, so DON´T TRY IT.
Earlier, population loss for completely residenceless kingdoms was not based on recent population, but 1/3 of the total land / hour instead. So a kingdom with 2k land could raze all his residences, then kidnap a bit every hour, and also train soldiers which he disbanded into new population, making the population increase extremely fast after a while. The money the unsupported civilians would produce would cover all the costs of training soldiers, and also generate a lot of excess money, making it possible to train TF´s and other unsupported military, so this strategy wouldn´t require that the player gained any new land at all. If starting to use it two weeks into a game, a kingdom would theoretically had been able to get a higher NW than the rest of the universe together only from the income he produced in the last day of the game. But remember that BCart has made this strategy useless now, so it won´t work any more.