Prime your nails with a base coat. I use a nail strengthener.
Paint two messy coats of white polish about half way down your nails.
Dip the small paintbrush in acetone and use it to erase the white polish until the tips are the width you want and have a smooth edge. Dab off excess polish and acetone on a paper towel.
Here's another picture of a nail in progress :)
Finish your manicure with a coat of quick dry top coat!