I have tried this technique a while ago in a pedi, but never attempted a manicure before. There was definitely some trial and error involved. First, I'll tell you how I did this, and then try and give you some tips!
First I started with one coat of OPI My Boyfriend Scales Walls... let's take a second while I gush about this polish... Perfect grey-ish white, great formula, love it! I had seen a lot of my favorite nail art bloggers use this polish over and over again so I knew I would have to get it. Every white polish I have ever used is really so streaky and annoying to use, but this one went on very nicely and was so easy to work with. I didn't have to put it on thick just to cover the streaks. I highly recommend it!
Okay, back to the design. I started with one coat of My Boyfriend Scales Walls, and then one finger at a time I added a second slightly thicker coat of the polish (so it wouldn't dry too quickly on me while I was working). I didn't glob it on, but I put on a thicker coat than I would have for just normally painting my nails.
When it was wet, I had my Finger Paints Ch-Art-Coal Black Striper open and ready to go, and put on 4 or 5 stripes diagonally up the nail. These do not have to be neat looking stripes, as you can see by my picture below. These stripes should be a little on the thicker side as well so that it blends together and it makes the next step a bit easier. Again, you don't have to glob it on, but I noticed that if I used really thin stripes without much polish I didn't like the final product as well.
As soon as you finish adding your stripes, grab a needle and drag from the bottom corner of your nail, on a diagonal outward to the tip of your nail. Repeat this process until you have the desired look that you want.
A few tips that I have is to use a light touch when dragging the needle across your nail. I noticed if I wasn't steady and pushed too hard that I would get some of my bare nail to show underneath. I tried to do this technique with a toothpick and it wouldn't work for me. Every time I tried it with a toothpick I could see SO MUCH of my bare nail, and it didn't blend the colors as well. I know some people have used toothpicks before, but it just wouldn't work for me at all.
Finally, I added a coat of Seche Vite to smooth everything out, and added little orange rhinestones into the corners of my nails. Thanks for looking!