Blacklining is a technique I find very useful. It gives the miniatures a lot of depth.
My way of blacklining is a bit unusual. I've never met anyone who does it the way I do. Anyway here goes:
1. Prime the mini white.
2. Paint black lines where you want the blacklining to be (don't worry too much about being neat). Unfortunately I've only got at pic where the skin is already painted.
3. Basecoat all areas leaving the black lines showing.
4. Shade, highlight, etc. as usual
See - It's that simple!