Avoid battles whenever you can. They're costly. If you can't steer clear, though, try to start things out with a stealthy attack from the shadows. You can always lure a foe to your area, as well, by making a bunch of noise. Then, as the unsuspecting villain gets near, you can attack from a safe point and snag an easy victory. Of course, this won't work if you're outnumbered.
Building Strategies
When you're building your settlement, keep in mind the old rule: location, location, location! Make sure your base of operations is on the lowest level, and pack your space tightly so that people don't have to wander needlessly and waste time. Make sure that you keep up on repairs, as well, particularly as winter approaches and makes survival more difficult.
Food Is Precious
Sometimes, you'll have all the food you need. Often, that's not the case. Therefore, it pays to be stingy so your resources will last. Feed people only when you must in order to keep them alive. You can get by with paying them only every other day or so, which is a good idea even if you have excess resources at the time; that could change down the line.
Scavenging Is an Art
When the time comes to scavenge, you want to send out whoever has the largest backpack. A second consideration is running speed, and you want to make sure you leave no later than 3 or 4 in the morning, depending how close you are to the exit. Fill your pack with food and components, wood, and medicine. Start by exploring those areas that are least dangerous--especially if they contain the above resources--and branch out beyond that only as necessary (and if you have room left in your pack). Finally, make sure you bring along tools that you can use to make the scavenging process go more smoothly. You'll lose some space, but you'll be more effective.
Sleep by Day
The most important time to be on your guard is at night, when the environment outside is most treacherous. You want to have your population well rested by that time, so they can guard against potential issues. Have people sleep when it's bright outside, but make sure you have someone crafting gear to help with the war. Then have that individual sleep at night, while his companions are handling the defense.
Start At Home
As you begin a game, your house will contain new loot and residents. Some of the latter may need to be healed, and you'll want to get to work building improvements with any of your materials before someone raids you and potentially takes your resources.
Battle Survival...