There aren't many good tactics for this level. One of the best tactics I found, you can't use often, but it works; if someone is shooting at you from the sniper balcony, run directly under it. If you are right against the wall, they can't aim down and hit you... but you can hit them with ease.

Another tactic, is if you're caught in an open room battle, to try to circle your opponent while firing. This will make it harder for them to hit you. Of course this is harder if they circle you too.

If you're on the bottom level, watch out for opponents shooting at you from the top level, they can easily catch you by surprise. Same thing If you're on the upper level, but it's harder for the lower person to hit you.

More action takes place on the bottom level where all of the starting points are. You will most likely score more kills down there than you would at the top.

One of the better places to be is on the upper level, near the body armor. You can duck away and grab body armor often, while covering one of the ramps. Just be careful that someone doesn't sneak up from behind you.