Tips on painting?

So, I just got some more Legion minis, I've built some originally but never got around to painting them yet because of other projects. Does anyone have any simple painting tips? Specifically for Clone troopers, Death troopers, Scout troopers, Magna gaurds, and/or Shore troopers? I've been putting off the painting process more even though im ready because im worried ill screw up on the most important part of the figure, the look, and i womt know how to fix it. Im most worried about the masks/goggles/breathing apparatus of figures since its so tiny and I haven't ever worked on anything that small before. I had just finally gotten some Vallejo acrylics for christmas and ive been wanting to test them out, but thought I should ask here first.