Rules of Thumb For 3D Work

Here are a couple of rules that you should usually follow, not in just Blender, but in any 3d program.

Modeling:

1. Make all of the polygons roughly the same shape and size.
2. Make sure that you do not have doubled up verticies or polygons.
3. Try not to make a triangles(This applies to Blender - I'm not sure if this applies to other programs. Please comment if I am wrong).
4. Keep good topography.
5. USE A REFERENCE IMAGE!!! This is a must!

Texture:

1. If you are using an image, make sure you are not stretching it. If if is stretching try to UV unwrap it.
2. DO NOT MAKE ANYTHING BLACK!!! This one isn't very obvious but its one that a lot of people mess up on.
3. Don't allow specularity if you have a shiny material.
4. Don't make a busy texture.
5. Look at a reference image.