Choose a glitter polish that is not rough when it dries. The one I used for this tutorial was rough and the effect was not very nice
Paint your nails with two coats of glitter polish. Make sure the polish has completely dried before you put on your solid polish
Make an outline of 'C' from the bottom of your nail, leaving a crescent like space. Then paint the remainder of your nail with your chosen polish.
It's a bit tricky at first. What you can also do is to paint the sides of the nails going forward and then paint the middle part.