GHQ, maker of those fabulous microscale armor and ships has a tutorial on making ocean hex tiles. The techniques also could be applied to other terain forms, such as those large styrofoam squares so many seem to use.
Modeling
Building Desert and Martian Terrain
This video describes how to build some terrific looking desert and Martian terrain.
Making Acacia Trees
WarFactory has a tutorial on making African Acacia Trees.
Basing Figures With Baking Soda
A mix of baking soda and super glue can be used to make finely textured bases.
Using Sculptamold To Make Wargames Terrain
I have used this stuff for years. It’s amazing.