If you get an airbrush, grab some plastic armymen and practice on them.

Another plug for an airbrush and vallejo surface primer.

Rattlecans are the worst.

I love Army Painter primers but I also live in the desert. If your climate is dry they work great. If you live somewhere humid they tend to come out a little "textured" when sprayed.

Dupli-color sandable auto primer!

Its the flipping best and comes in a range of colors for only 5 bucks a can.