For me, I do a lot of research before the build begins. Since most photos are in black and white, it's sometimes hard to get a scheme absolutely correct.
When I do a camo scheme, I have a basic idea in mind but, I let my imagination take over (as if I were part of the tank crew and how I would want my tank to be painted) I never have it set in my mind that, this zig is going here and that zag is going there. Mostly just freestyle with my airbrush.
As for something totally off the wall (like a Glossy Metallic Pea tank for instance) I agree with U-96's statement. I wouldn't want to experiment with a $45 Tamiya kit.