TEXTURES
I do make my own textures. See de_salt(2) & de_kalt for reference. Also a new map coming soon will have all new textures. (Not really new, just unreleased :)

I use Paint Shop Pro 5 to make them, and then Wally to wadify them.

Here's the steps I usually take to make a texture:

1. Find a photo on google or use a digital camera. Should be very high-res.
2. Crop to a square, but keep the original image for cloning.
3. Get it to wrap left-right and up-down. I use a lot of clone brush for this.
4. Smooth out any 'landmarks' in the image so you can't see it repeating over and over. Sometimes just erase them, or clone them in a non-uniform pattern. <-- also lots of clone brush.
5. Maybe sharpen or recolorize. If the image contains large dark/light regions, I use inverse low frequency blending (below).
5. Resize to 256x256.
6. Reduce to 256 colors.
7. Copy/paste into wally.


Inverse low freq. blending:
Sometimes no matter how good your texture wraps and how detailed and good it looks alone, when it repeats across a wall or whatever, it looks like shit because, for example: the left half is dark and the right half is light. So: vertical stripes.

For this problem I like to use inverse low frequency blending (ILFB).

Alls you gotta do is:
1. Blur the image A TON until its nothing but a smooth gradient reresenting light/dark regions. I use a gaussian blur with a factor of like 15.0. This gives you just the low frequency image data.
2. Take the negative of the image. Now you have the inverse of the light/dark regions.
3. Re-colorize the image so it matches the original color (about) but with backwards lights/darks.
4. Blend this with the original image. I use a mathematical average in PSP5.
5. Fix the result by hand and with sharpening (probably). It should no longer have light/dark regions because they should have been canceled out in the blend operation.


MAPS
I usually draw everything on paper before I do it on a computer. This goes for maps, coding, web design etc. This doesn't mean I'll follow the paper plan exactly but it helps me to organize my thoughts in sloppy ink markings before I try to build the final poroduct.
But that's just me.