1. Paint nails a base colour, a colour a bit browner than the one I used would be better!
2. Then randomly paint some dots with a brown nail varnish
3. And finally paint some lines around the brown dots with some black nail varnish as well as some little black messy dots by themselves.
4. Finish with a clear coat.
This is really really easy to do and just to prove it, above is a picture of my right hand and we all know how hard it is to paint your nails with your left handed if you're not usually that handed.