This is a tutorial that I wanted to do but left it late in the day to photograph and so it was a rush job before the sun went down so please excuse the sloppy look of the nails it should have looked a lot better.
1. Use any two colours of your choice making sure one is lighter than the other to see the contrast in colours.
2. Paint the whole nail first with the lighter colour I would normally use a base coat as this stops nail polish from staining the nails and gives something for the varnish to adhere to.
3. When polish is completely dry (which is what I did not do) apply cellotape to one nail not the strong stuff as it peels of the varnish, on a slant or however way you want the effect then apply the darker polish as soon as you have done the one nail remove the cellotape slowly straight away, apply this process to each nail one at a time. My tip would be to cut ten pieces of cellotape ready to apply on the edge of the table or something as it is a nightmare trying to do it with wet fingernails.
The end result funky nails if I had more time they would have looked awesome!
If you want your hard work to last longer apply a top coat!