These are the supplies you'll need, plus some nail varnish remover!
Start by applying your base coat, I've found that white or nude look best, or maybe a nice pastel colour!
'Drop' a little of both of your other colour varnishes into the water. I've used blue and pink.
After a few seconds the varnish will start to spread across the surface of the water and turn into a kind of 'film'. It's important that you wait for this to happen...
Dip your finger in so that the varnish grabs onto your nail. It can take a little practise and be a bit messy. So have some nail varnish remover handy! Wipe the excess from around the nail with q-tips
You'll end up with these marble effect nails. Finish with a top coat of clear varnish. I've found that pastel colours on top of a white base coat also look really cool... Have fun!