Easy Peasy Chevron nails

If you have tape and two colors of nail polish, you're good to go.
First paint your nails a base color.  I tend to use the less-flashy one for this, but as long as your boat is floating.

I used the one on the left (Thanks a Latte by Spoiled) for the base, and the gold one (Golden-I by Sally Hansen) for the chevrons.
Make sure your base is dry before attempting anything with tape.  I've almost gotten to where I wait until the day after to do anything extra on top of an existing coat, because if your polish is even kinda wet, that tape'll suck it right off.
Once you're dry, pull off a piece of tape, making at as square as you can.  Put it on your nail with a corner facing up, almost reaching the top of your nail but not quite.

Then you start painting your accent color in the area left open by the tape! Technically you can paint the whole nail, but since it's all coming off except the chevron, I just concentrate where the tape isn't.
You'll need to wait a good while before you take the tape off, and be careful when you do, because sometimes it will take parts of your design off if you're not careful.

You've been chevron'ed.