A lot of this is engine and game-type specific, but commonly works with most games.
Visibility refers to how much the player can see. Games have limitations to how much can be seen on screen at once, and you will have to build around it creatively to look as detailed as possible without a significant drop to frame rate. It can also be used purely artistically for a grand reveal such as exiting a tunnel into a beautiful mountain scene. Casino layouts are often a warped and distorted maze to keep the customers in as long as possible.
A few classic examples of blocking visibility:
The S-Hall is using an "S" shape between two rooms. This is the most basic visibility break between two rooms. The S hall has two close relatives, the Y-hall and U-hall.
The I-Hall is essentially breaking two rooms with a big letter "i". It is a great because it always works and gives the player the illusion of choice as well as double the play area as an S-Hall.
There's limitless ideas from there just be creative with your visibility.
Deathmatch Level Design Study
Man to man combat based is reality takes place an arena type environment such as a boxing ring. An arena can be any large open area. Most levels are a series of connected arenas with the total number of arenas based on number of players or events to happen within that level. These are the fun rooms, where the big things happen.
Things that help make a level fun:
A room with at least two floors. The multiple floors allow for vertical combat Snipe your enemies from above or stalk them from below.
-Three ways to get between those floors. Be it stairs, ramp, elevator, jump pad or teleporter, the player must be able to navigate the room quickly and smoothly.
-Three exits is a great starting place for a fun deathmatch level. Three exits ensures an escape plan.
-Columns and propping. What better to hide behind in a quick situation, and make the level appear strong and supported? Crates is the classic prop to hide behind. Be creative and build unique objects that better tell the story of the level.
Here's an example room featuring those concepts.
TIP: Build a human ref. It can even be a box, as long as it's the scale of the player character. This will help in judging the size and shape of things.
A larger, second room.
Putting the two together by creating fun, small rooms out of the visibility halls for final result.
Download final version in .MAX 8 and .3DS format
Test early, test often! The more that's right from the start, the less you have to change in the end.
This is only the basic gist of deathmatch level design. The best ideas come from testing and designing the most fun environment to suit your game play.
More on this later...