When painting armour
Use Tamiya NATO black as the base coat rather than primer. It gives your top paint job some depth when you paint it and don't get a wholly even coat
This is a NATO black base with a Dark Yellow coat...if I wasn't doing camo, it's ready

This also helps for any rubber on your wheels
No need to mask your wheels - just turn the pressure down on your compressor and reduce your paint flow and with a steady hand, you can paint the wheel with relative ease AND you're left with that worn, touched up in field look
Admittedly I could've done better here - but you get the gist

Also in the first image, I've got the skirting on the tank. I haven't stuck this down across the whole of the tank...I've put them on with a dab of glue at both ends so I can take them off. The reason I've done this is so I can have an even flow of camo