• Only use a single Weapon. That way you always get Ammo crates for Ammo you'll actually use, so the chance that you might run out of ammo is lower and you save some money you'd have to spend on ammo.
  
• Try to only buy barricades, turrets, weapons and ammo when on sale. It's randomly chosen every night what will be on sale.
  
• If possible, only buy steel barricades. That way you'll actually save money because steel barricades withstand more damage and you'll have to less frequently replace your barricades.

For most achievements I used this strategy. When you build fences, build them like this:



That way Zombies can't walk through them (or at least they never did) and you're still able to easily pick up everything they drop, since you're able to walk diagonally through them. If you want to build steel fences, replace the wooden fences beginning at the inner.

Another possible setup:

Survive 6 nights without buying anything


There isn't really any strategy behind it since the achievement requires you to not buy anything. Just walk around in big circles around the lantern and try to keep a good accuracy.

Survive 10 nights without any barricades or turrets


Just do the same as for Saving Up and don't buy anything. After 4 or 5 Nights you'll have enough money for the Tesla or after 5 or 6 Nights you'll have enough money for the Laser, just buy the one you prefer, but don't buy any other weapons, that way you'll always have enough ammo thanks to the crates that drop. If a zombie drops health and you need some, just walk a small circle and shoot your way through to be able to pick it up.

Survive 10 nights without taking any damage


At first I thought I'd never get this achievement. Well, wrong. All you have to do is Host a Multiplayer Match, build lots of fences around you, let your buddies pick up all the stuff and stay safe inside the fences.

Kill 8 zombies with a single sniper rifle bullet


I tried to do the same strategy as I did for Demolition and shoot them diagonally, but that didn't work for me. Instead I built two lines of fences around the lantern as in the screenshot below, still leaving out one fence on each corner to still be able to walk out. Just wait until enough of them are in line, then shoot your way out and shoot the line of zombies. Don't build any turrets.



Kill 8 zombies with a single rocket


Don't use any turrets, they'll ruin this. Since Zombies get tougher they won't be shot with a single rocket after a while, so your goal is to buy the rocket launcher as soon as possible. Build the fences as suggested in the first section of this guide and collect the zombies around in a line around your fences. When you walk near a Zombie he'll follow you and you can kind of position them. To be on the safe side, collect more than 8 Zombies. If you have enough of them gathered around, just shoot a rocket directly in the middle of that mass.

Kill 300 zombies with shotgun in a single game


Just buy some turrets and mount them with Shotguns. Yes, that counts. That's actually all you have to do, after a while you get the achievement. Don't buy any other weapons, since that way you can get more Shotgun Ammo from crates.

Use no more than 6 clips during the first night


Start a single player game, don't miss any of your shots and never reload manually. Every zombie will be killed with 4 shots. That's it.

Build and equip four turrets


You'll get this eventually by just playing the game. Build fences like above and place a turret, one by one directly around the lantern.

Score 1,000,000 points


Just as Come get some, you'll get this achievement eventually by just playing the game. Build the fences like suggested above, get Auto-Turrets when they're on sale for 6,000 $ instead of 8,000 $ and mount them with a pistol until you have at least four of them, since they don't need ammo. Replace them with a better weapon when you're able to, but never use more than one weapon, since crates contain random ammo of weapons you own, that way you'll only get ammo you'll actually need.