Just like to make a couple of points as a military pilot who flies a lot of GA as well.
Noggin makes a good point about keeping the circuit to a sensible size, and running the wingtip down the runway is a good idea (if you're in a low wing aircraft); as is using the 45 degree point to turn finals (as a Jet Provost QFI we picked a point 45 ahead and on the extended centre line as a roll out point.
The main problem I see a lot is not the actual size or shape of the circuit (love those oval ones though), it's the fact that sometimes you get half a dozen aircraft flying half a dozen different sizes.
Run in an breaks - a quick method of a getting an aircraft down on the ground if you're coming in at 250kts+. not much use in a C152.