Here’s a photo tutorial on making a terrain cover from cloth and latex caulk.
Modeling
Building A Shanty Town
For those modern and near-future games, here’s an illustrated tutorial on making a really neat shantytown.
Making Concertina Wire
Here’s a great tutorial in making some very realistic concertina wire for your 25mm – 28mm miniature games.
Making Terrain From Cardboard
Although this video is focused on Warhammer 40K, I think the techniques shown for building terrain entirely out of cardboard are worth studying.