Spreadsheets
It is a good idea to take notes in word and excel 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.

Powerless Mountainous
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
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, even on a target. You will have to kidnap population to stay alive after this.

Depressland’s residenceless+barracksless strategy
With this strategy, you raze all your residences and barracks a short while into the game. Your population will then leave you, but only 5% of it every hour.. you can therefore 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.
A good time to go residenceless is after you have much land and TF's researched. No one can compete about the no.1 NW spot with a player which has 12 mil/hour in income and trains 300k TF's/day unless he plays that way himself, so this used to be the ultimate end-game strategy. In SK 2.0, the population losses are increased a lot when being residenceless, so it's likely that it will be far harder to play this way now.

Residenceless, powerless and barracksless combo
You combine the two strategies above. Both residenceless, barracksless and powerless means a lot of extra land for Star Mines.

Immediately residenceless and powerless
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
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
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 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
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
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
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
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
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.