I've never had any luck with those itty bitty nail guides for french manicures, so I was looking up some other DIY methods for french mani's and came across the idea to just use scotch tape. Easy, cheap, and most of us already have it in the house!
All I did was take a strip of tape and start at one edge of my nail and as I went from one side of the nail to the other, I let it follow the natural curve. The tape will buckle from making the curve but as long as the edge is pressed tight against the nail, you won't have any polish seeping underneath. I taped all ten nails, applied two coats of polish and let it dry. Then peeled off the tape and finished the entire nail with a topcoat. You can see on my pinky that the topcoat picked up a little colour and smeared it, so I will have to let it dry a bit longer next time.
Give it a try! I think it turned out pretty well for a first attempt and now I can get a french without having to shell out extra $$ at the salon.