I did these pictures and manicure ages ago but just found them now. OPI also sells a crack nail polish and I think its pretty cool and something different.
1) Give yourself a neat little manicure and paint a clear base coat
2) Choose a colour you like and do two coats of that on your nails.
3) Ensure your nails are dry and paint ONE very thin layer of the crack varnish over the colour. Do not overlap the crack as it will turn into a mush. It doesn't have to be perfect. Let it dry and watch it crack.
4) Paint a top coat over the crack to seal it all in.
I think it looks pretty cool.