Things I have learned that new rimworld players might like to know:
"Cover" in this game works more like "concealment." Being positioned behind a sandbag wall means incoming fire has a 65% chance to hit the wall instead of you, but if it hits you, it can hit you anywhere - even the feet/legs, which logically should be impossible.
In a pinch, stone chunks (not bricks, but the raw chunks) are almost as good as sandbags. (50% cover). Even regular furniture and workbenches can provide cover.
Friendly fire has a minimum radius of 3 tiles. A pawn can safely shoot "over" two allies in front of him.
A good way to set up a defense is to build a sandbag wall, put a melee fighter (with a shield belt, ideally) right against the wall, and a ranged fighter behind the melee fighter. That way, if any enemies close to melee range, they will have to deal with the melee fighter first, who is ready for them. This also allows the ranged fighter to keep shooting uninterrupted.
Don't put a structural wall behind a sandbag wall. When raiders start showing up with incendiary launchers and rocket launchers, this will cause them to hit you even if they "miss" because they will hit the structure wall behind you and their projectile will explode.
A melee fighter with a shield belt is not cover. Shield belts don't work the same way as sandbag walls - they only stop bullets that would have otherwise hit the belt wearer. They will not stop bullets from hitting someone standing behind the belt wearer.
If you want prisoners, try to use blunt melee weapons made out of wood. They are more likely to have non-lethal takedowns than sharp weapons (and all ranged fire counts as sharp), and wood swings more often with less damage per hit. If you use heavier material in your clubs/maces such as stone or steel, they have longer cooldown times but do more damage per hit, which means each individual hit is more likely to cause fatal damage.
Your animals WILL eat your drugs and alcohol if they have access to them. It's a pain in the ass to keep them sequestered from them, but you gotta do it.
Also, be sure to set your drug policies to limit use of recreational/social drugs to no more than once every 2 days and only if mood is below 45%. More often than that risks developing adverse effects - smokeleaf causes asthma, which is incurable but manageable, beer causes liver problems, and harder drugs have myriad drawbacks. Ambrosia is relatively harmless but is extremely addictive, and withdrawal is a bitch when it runs out - and it can't be planted, it can only be harvested wild and it only sprouts rarely.
If you have colonists carrying guns (or melee weapons with high melee skill), don't forget to switch their threat behavior from "flee" to "fight." Otherwise, they will not deal with any threats unless manually drafted.
The "Wimp" trait can be a blessing for non-combatant characters. Raiders, mechanoids and non-predator animals will most often ignore a downed pawn and move on to the next target, and "wimp" makes a pawn go down quickly, thus potentially sparing him from worse injury, assuming the rest of the colony isn't overrun and he gets rescued.
The "BZZT" emergency (your batteries cause an explosion) can't happen if you don't have any power conduits, as it is the conduit that explodes, not the battery. Early game, this can be avoided by simply building your batteries right outside the wall of where you need power most, and then building your solar panel right up against the battery. Appliances on the other side of the wall will plug directly into the battery through the wall. Remember to extend a "roof build zone" over the battery to keep it out of the rain, but don't cover the solar panel.
For that matter, make sure all your batteries and electrical appliances (especially smelters and crematoriums) are under a roof, even if they're outdoors. If they are powered on but exposed to rain, they can short out and explode.
Soon as you can, get the fuses/circuit breakers mod to deal with the BZZT events.
Never recruit a pyromaniac, if you can help it.