Sneaky tip #1--Boomers can be placed on walls. I have even heard of someone putting one on a ceiling, but I have never been able to do it...yet
Sneaky tip #2-- When you drop a mine in a fairly open space, like in front of a door, etc.., step back a little then drop a spare ammo crate. This will effectively hide the mine (at worst partially hide it) and the rat trap is set. Grenade ammo crates work real well because everyone seems to try to pick those up. I don't do this too often because I don't like to waste ammo, but it does work like a charm

Sneaky tip #3-- You can place Spitfire Turrets on the squares of cement along the outside wall of a base. This is really good for raining down bad news on infantry hugging the bottom of the walls.
General tip-- If you have mines set up at choke points, check your map often to make sure they're still there. If you haven't been racking up kills, and they're gone, someone's been taking them out.
HANDY TIP FOR ALL SQUADMATES: (I borrowed this from one of the forums)
/alarm is a built is stop watch in the game. As soon as you hit it the window pops up. I keep mine set at 15 mins all the time. So each time it will start at 15 and all I have to do is hit set and the stop watch will start to count down. Not only will it count down but it will also give you small pop up warnings as the time gets closer to zero.
Anytime you want to know how long until the base is hacked - you don't have to ask everyone a million times or even be in the cc. Just type in /alarm again and the stop watch window will pop up and show you how much time is left. It stops giving you little warnings at the 5 min mark.
Thats all the tips I have to share atm.