first off the air brush has a mind of its own ! some days it wants to work better then other days. If you find your self getting up set because the brush or your hand is not working right that day, take a brake and go do something else.
Make sure that the air brush is clean, if not the air brush will not work right, and this will mess up your work and piss you off, I know first hand !!!!
The brush will clog off and on, but don't worry it is normal for it to do this. If you find that it clogs all the time thin the paint. and make sure the paint doesn't have big clumps in it. You can strain it with a nylon or a small paint filter.
For big jobs like walls I use bigger cans of oil base paint, for black I use krylon flat black or rust-oleum flat black. the same with the whites I use a bright white. Oils work best for this but you can switch off with latex colors. But latex clogs up the air brush more the oil.
The templets can be made out of card board or I use thin plastic that I
get from work. I cut them on my scroll saw into the shapes I want....