For the next two terms I will be working on my very own custom (UT) Unreal Tournament Multi-player Map (level). I was quite happy when I was told this because I feel I have a lot of knowledge of this type of FPS (First Person Shooter). The key to all great FPS maps is game pace and balance.
I'm going to stick the the conventional style of Unreal Tournament which is very fast pace. Because of this fast play style there are significant differences between levels in UT and Counter Strike: Source for example.
In this picture you can see the spawn point of one of the games more powerful weapons. The risk of getting this weapon is that it is surrounded by bio waste which does damage to you when you stand in it. This creates risk to achieve a benefit. You could get knocked into the bio waste by enemy fire on the way there and there is only one route out as well which means any enemy's will know which direction you have to go to get out. The same can be see in the picture below.
In this picture there is the most powerful armor upgrade in game, but again you must risk jumping onto a small platform which is surrounded by bio waste.
Because of the fast pace and splash damage most guns in this game have cover has to be more obvious and easy to use. Rather than having small walls in which to crouch behind (which encourages camping, thus breaking the speed of the game) cover is large and obvious. These blocks in the middle of the corridor can be easily jumped behind to break an enemy's line of sight (LoS) and therefore only leave you vunerable from splash damage.
Also the majoirty of times you will use cover is because of an enemy having an advantage over you. This can be from an enemy having more health than you or them having a weapon that is most powerful at a range but not upclose. By hiding behind boxes like these you're forcing you opponient to come closer which can take away there advantage.