This video from Red Beard Baron is a good tutorial on making a wargames mat from cloth, cauking and flock.
Modeling
Making A Wattle and Daub Wall Wargaming Terrain
Here’s a photo tutorial on making a wall that simulates the wattle and daub building technique.
Early Crusader Period Flags
Here’s a selection of early crusader period flags.
Making WWI Airplanes From Clothespins
This post on making WWI aircraft from clothespins is not really a set of instructions, but the photos show clearly enough what has to be done. Brilliant bit of model making.
Model Trees and Silhouettes
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.