Before we start on how to best optimize your map, you may want to fully know what you can expect from optimization. It's no use reading through this entire tutorial to find out at the end your problem can't be solved using optimization. So, here goes.

Optimization allows you to simplify your map. Done right, this can save on compile times (the time it takes to build your maps) and/or ingame speed (known as fps, frames per second). Done wrong, optimization can actually worsen the way your map plays, or increase compile times. You have to remember optimization doesn't do wonders. Build your maps with the tips in this guide to make sure you don't end up with a map that runs horrible nor can hardly be improved because of wrong planning. Optimization takes time, you shouldn't expect to get an amazing ability to make every map run at 100fps on a geforce 2mx directly after reading through this guide. Be patient, experient yourself, and you should atleast know how to go into the right drection. Some people will never get the hang of optimizing.

If optimization is an University-grade study, then mapping and scripting entities is kindergarten.

Common terms you may not know but will encounter:

• World brush: a brush that isn't tied to any entity
• Skybox: the collection of "tools/skybox" textured brushes that cover the top of your map, giving the appearance of a sky
• 3d-skybox: see above, only instead of an appearing sky projects another part of the map
• Framerate, or FPS (frames per second): how fast your map runs, the higher the smoother, the better!
• Compiling: To turn an editable map into a playable map
• vbsp: The first compiling program, takes care of general BSP structure, and portalling
• vvis: The second compiling program, takes care of visibility, can take hours on an unoptimised map, luckily can also take seconds if optimised right
• vrad: The third and last compiling program, takes care of ( the static ) lighting your map
• bsp: Binary space partitioning, basically a format to write and use maps (originally ported from Quake)

I will often refer to NODRAW-brushes, CLIP-brushes, HINT-brushes. By them I mean brushes with their corresponding "tools/tools*" texture.

If you find terms or words you do not know, look them up using www.google.com. This is, after all, a university grade guide :P
If you think some important terms are missing then please contact me about it.

All of Valves example maps can be found here:

Your steam drive:\your steam directory\your steam username\sourcesdk_content\hl2\mapsrc\

My example map can be found here