Airbrushes are great for lots of things, but they also take lots of maintenance. Here’s a tutorial on how to clean your airbrush.
The Wargames Table has a nice article on touching up some basic resin walls to make them look more realistic.
Pinatwar has a useful post on painting fur.
The 1000 Foot General has a photo tutorial on painting skeletons from Reaper’s Bones line.