Recently David and Chris have posted modeling tips. I don't want to be left out, and since they each posted one tip, I will outdo them and post two.
Burn Baby Burn
Most modelers use washes to weather parts and to emphasis panel lines. Acrylic sludge washes are common, as are watercolour washes. However, many modelers like to use artist oil paints. You have a few options to thin your oil paints for washes, and the use of Turpenoid is quite common. However, I prefer to use Naptha lighter fluid. (The brand name on my bottle is Ronsonol.) The lighter fluid thins the paint very well, it evaporates quite fast so it shouldn't damage underlying the paint, and it is also very thin, which allows for very precise application into panel lines. Not to mention when you decide to end it all, just spray the Ronsonal all over your work bench and kits, light a match...and...well... modeling will no longer be a problem...
Let It Flow
Like Polly Scale's choice of colours and easy availability in most hobby shops? Hate how they airbrush? Well check out Liquitex Flow Aid. I add eight or so drops to every jar of Polly Scale when I open it. The Flow Aid improves how the paint goes on by brush. I've also noticed that if you thin the Polly Scale with 40% to 50% Tamiya thinner and add a drop or two of the Flow Aid that you can get the Polly Scale to spray without tip clogs. Oh joy!