I've been told that not a lot of new textures are being made these days and I'm thinking about working a on a texture set or more if anyone actually uses them. I do graphics for a living but I've never done textures for games before. After a few tests it seems like a lot of fun so I might go ahead.

I have a few questions tho, because in the tests I've done, the textures don't quite look like what I expected in-game. Contrasts seemed different and some colors came out more intense than intended. I know the size needs to be in multiples of 2 and should be tileable, but that's about it.

Is there anything else important I should know about? Any tips on how to make them look better in terms of contrasts and colors?

I haven't really done textures on my own (i only altered existing ones), but evillair has some good tutorials on creating textures and to give them some realistic feeling.
http://hfx.planetquake.gamespy.com/tutorials.html

He also created a platform especially for texture-creation for games.
http://pixelmorgue.com/forums/

Thanks for your reply Mr. Strahlemann. I will definitely take a look at those forums.

The thing is, I know my way around PS but I was confused by how different the textures looked while in-game. But I guess I just have to make some more tests. I think what might be a good way to test is to pick an existing map that is well lit and replace it's textures with mine to see how that looks.

Starting this thread might be a bit premature, sorry about that. Nonetheless, if you or anyone has more suggestions or links please go ahead.

nexuiz textures are made from few gfx files

texturename.tga - color map (because many ppl runs nexuiz w/o bump maping it should have some shading and little bit of highlights imho)
texturename_bump.tga - bump map http://en.wikipedia.org/wiki/Bump_mapping
texturename_gloss.tga - its gray scale like bump map but it tells where to put highlights (and how intensive)
texturename_glow.tga - everything not 100% black here will ignore lightning on a level, its useful for parts of texture that looks like its emitting own light, in pitch black room, only this texture will be visible

there is texturename_norm.tga too, http://en.wikipedia.org/wiki/Normal_mapping but its better than bump map only if you generate it from 3d geometry (nexuiz still needs bump map in normal maps alpha channel to use it for parallax mapping )

i hope it helps and i cant wait to see your textures