The single most important as well as overlooked problem that new level editors make is ignoring the r_speeds of their levels. A highly detailed area with a large number of brushes will slow down the frame rate of your level. Keeping frame rates low makes the difference between a good and professional level editors. Here are 3 basic commands you can use from the Quake console to check your map and see how complex you have created areas and where you can improve on. Note - make sure you VIS your level before you use these.

r_draworder [1/0]

This command will let you see everything that Quake draws on the screen. Normally Quake will draw from the farthest point to the closest, blocking out some of the extra things that Quake might draw. This reverses so that you can see where you might be losing frame rate because of bad layout of your map.

r_drawflat [1/0]

An incredibly useful command, not only for finding slow points but also for looking at other people levels to see how they have organized their brushes. r_drawflat 1 will remove all the texture and replace them with solid colours. You can then see where QBSP might be cutting up some of your brushes into hundreds of other brushes. Those arches you had gotten down to six brushes might end up being thirty after QBSP gets at them.

r_speeds [1/0]

This is by far the most useful command. When you type r_speeds 1 in the quake console it will begin printing out a set of numbers that look like :

The numbers most important to be aware of is the group of three. Specifically the total polygons in view. This number you want to keep at a minimum - less than 500 is a good rule to go by.

A Dynamically lit surface is a face that is lit by a light which flashes, strobes, pulsates or in some other way changes. Dynamically lights have a large effect on frame rate during game play and you will probably want to only use them when necessary, and then only in remote areas.

Also, it is _definitly_ worthwhile to check out the WCU class that Somberfire gave on r_speeds. Lots of great information on how r_speeds works and how to keep them low.

And, DEFINATLY check out this article, Designing levels with speed in mind. writen by Steve "Gateway" Tietze of Rogue Entertainment. Very well written and detailed.