The Quake Community site Quake3Bits has published an extensive series of video tutorials on terrain creation in Blender and on exporting the resulting model to Quake. Obviously, they're aimed at the novice Blender user but they do go into subjects such as mesh modeling, assigning multiple materials to a mesh, UV mapping and UV painting.
From the description on the site:
"Nearly 3 hours of video walking through of the process of using Blender 3D to create low poly terrain models for games that support the creation and input of user made content. Although the final models are for use in idsoftwares games, the general usage of Blender to model objects is the same as it would be for other games; basically the general principles should hold true of any low poly modelling for any game that supports it.
There's nearly three hours of video available. If their server is slow, please give it a rest and try later.
Download the videotutorials here.