does anyone know any good tips for painting circles

[Ed]

I working on my mercs/khador stuff atm
with my steel heads/winter guard and i want to paint a icon on their armor from my favorite video game Metal Slug the icon that i am going to try to paint is http://villains.wikia.com/wiki/Rebel_Army

If anyone one has any tips it would be very help full.

[JakeM]

Thin the paint out a lot. That way it goes on smoother and is easy to take off or paint over if you mess it up.