What everyone else said, paint, paint, paint, paint.....and then paint some more. Study as many painters as you can, both game artists textures and classical painters. Grab a photo from online of some stone, or wood or something and try to paint it. Good luck!
Hand painted textures aren't systematic and procedure based like a lot of realistic next gen stuff can be. It's...well...hand painted, so what you want to look at is 2d painting technique. Surf around conceptart.org and check the work out there. You will need to be able to render texture, color and form, so pay special…
theres some pretty dec "how it was made" threads on conceptart that show some good techniques for coloring sculptures that could be applied to painting 2d textures. check em out..
I think the others have pretty much said what needs to be said but heres a little tutorial by a good Illustrator/artist on how he paints game textures http://www.michaeldashow.com/tips_texturepainting.html
Josh Singh also has a good tutorial. I'd take a good look at his work and Bobo's. Two of the best at hand painting textures IMHO. http://boards.polycount.net/showthread.php?t=47912#Post205019
TF2 is not any more hand painted than any other next gen asset. A lot of the old tutorial material is gone. Basically one good tip is to start with some nice baked lighting as a base. From there I usually smudge that around to get decent looking faked geo. Then layer stuff on top of that; colors, etc
Does anyone know of any good tutorials? I'm having a bit of trouble finding any. I did a search here but couldn't find much, and the web doesn't seem of much help either. I'm sure I am not looking the right way though. I really want to put some custom textures into my portfolio to make it more appealing. I was hoping to…