Section your hair into four ponytails. Do not just glop it on your head like shampoo. You’ll end up with a mullet of two tones. Start at the ends—they absorb dye faster—and work up to the roots. Roots are hot from your scalp and process quicker, so they hate being first.
Use a timer! Set it for the exact time on the box. Checking your hair every 3 minutes does nothing except make you paranoid. I once checked too much, ended up with root sparkles, and had to wear hats for a week. Not cute.