So this is my first attempt and my first quasi tutorial. Be gentle!
For a half-moon mani you need something like these circular reinforcements. This works like a scotch-tape mani and if you want it to be in a rounded shape these work awesome. I think I paid like $2 for a sheet of 560,
my earlier post.
Of course this being me I couldn't leave well-enough alone. So I added a very thin French tip using China Glaze Sea Spray.
Slap on a layer of top coat (I use Seche Vite) and you're done!