Paint it, nail it

Line your nails with petroleum jelly or white craft glue before painting 
If you're working on a nail look that's messy, use a cotton swab to rub petroleum jelly like Vaseline on the skin around your nails first. This creates a barrier between the polish and your skin so that after you've painted your nails, you can wipe off the Vaseline and any polish mistakes along with it.

To prevent the tips of your painted nails from chipping, paint two basecoat layers
Paint the first layer of your basecoat polish on the top half portion of your nails only. After your nails have dried, paint a second coat of polish, but this time cover the entire nail as you normally would. This technique will help the polish on the tips of your nails — which are more prone to chipping — last longer.

Use a white nail polish as your basecoat to make your nail 
color pop
Unless your polish is super opaque, the natural tint of your fingers will change the colour of your polish. To get the paint's true colour, add a layer of white nail polish first, and then go over it with your coloured polish.

Give your nails two-tone designs with tape
After you've chosen two different polishes, paint one coat of the lighter polish on each nail, and seal it with a clear topcoat. After it is completely dry, apply two strips of tape over the tips of your nails so that they cross in the middle and create a point. Take the darker of the polishes, and paint a layer over the entire nail and on top of the tape. Let it dry for a minute, and then grab both ends of the tape and slowly peel them back at the same time for the finished look.