The best way to make stripes on nails is with a liner brush. You can find a striper/liner brush at some beauty supply stores or even your local craft store. The brush will have long thin bristles, and when you get it wet with paint it comes to a very precise point and is no wider than a toothpick and about an inch or two long depending on what brand or style you buy.
As for actually making lines, it’s pretty simple but takes a steady hand. First, take the lid off the paint and swirl the brush around the inside of the bottle, coating all the bristles evenly and making them all stick together and come to a fine point. I’m right handed, so I always start from the left side of the nail and work to the right.The pressure you use will determine how thick the lines will be. If you need more paint, just dip the tip of the brush in the lid of the paint bottle.
— Jade Sewell is a nail artist at Just Nails in Great Falls, Mont.