The most challenging element is elevation. Chris Pringle uses up to three elevation levels and most of the scenarios see anything from 20-90% of the table covered in hills, ridges etc.
Now Chris has some suggestions on how to tackle hills and you can read them at his blog, here.
My own method is based on roughly rectangular pieces of cardboard cut to different sizes and glued with green, brown, and deep brown paper. The goal is to have a inventory of pieces that can be used to build different battlefields. They do not look nice, but they are cheap to make. Also you can easily make them look nicer by gluing sand, foilage etc on them (this will happen little by little). For steep slopes I think I will use the tactic I use for rifle pits and entrenchments and create little sticks with rocks etc, which can denote a steep slope.
I still need tons of green (lvl 1), brown (lvl 2) and dark brown (lvl 3) peices, but here they are used to represent Solferino and Beaugency.
Again, no work of art, but its a start. Foilage, steep hill indicators and sand will make them look cooler.