Mark Veneman has a tutorial on making model trees. He also has a useful selection of tree silhouettes to help you shape your little wonders. While the instructions are aimed at model railroaders, they’re just as useful for miniature wargamers.
modeling
Turning Doormats Into Hedges
Craig’s Wargaming Blog has a nice description of his method for turning doormats into hedges in twenty minutes.
Making Ocean Boards For Wargaming
Small World Productions has a tutorial on making ocean boards for wargaming.
Making Thatched Roofs
I’ve tried a variety of different methods for making thatched roofs for my miniature wargames buildings. This one from Ryan Skow works well.