Shave your legs 1
I highly suggest shaving your legs the day before you self-tan. It actually helps exfoliate your skin and removes any dead skin cells that can cause streaks.
Exfoliate for real 2
With that said, make sure you actually exfoliate the day before using a body scrub and soft cotton wash cloth. I really love Laura Mercier Creme de Pistache Scrub ($50). It leaves skin soft, smooth and polished. It also smells delicious!
Make sure you moisturize the rough spots on your body like your knees and elbows. This will help prevent any color buildup or streaking. Any would do, but I like Ludriderm Daily Moisture ($8). It absorbs in a matter of seconds.
Test a patch 5
Try testing out a patch on your upper thigh (which tends to be lighter than the rest of your body) to see if you're getting the color you want. You can experiement on your stomach too. If it looks more brown or bronze, you're good. If it turns orange, you might want to get yourself another self-tanner.
Use a mitt 6
Most self-tanners come complete with a mitt, which makes for better and more even application. But you can always buy them separate too. Try Tarte Brazilliance Mitt Duo ($12).
Use a lot of product 7
Don't be frugal on the self-tanner unless you want to find yourself with streaks and patches afterwards. Remember, applying more won't intensify your color. How deep your tan is solely depends on what color formula you bought, whether it's light, medium or dark.
Give yourself a few minutes 8
Stand straight and maybe even park yourself in front of a fan (slowly rotating) for a good five to ten minutes. That's about how long is takes for the color to set and dry.