Friendly warning: I do mean natural and subtle highlights. Brown or black hair might go red, not blond.
Step 1: How it Works
This is permanent.
It may fade with time, but treat it like permanent hair dye. Luckily, the color change is so gradual that it is very easy to control.
Step 2: Supplies
1. A bottle of real lemon juice (not lemonade).
I like the little lemon-shaped ones, the squeeze tops work perfectly.
2. A shower or water squirt bottle. Something to get your hair soaked.
3. A towel. A hand towel or washcloth is okay.
4. Sun protection gear. Specifically sunscreen and sunglasses.
5. A brush and/or comb.
Step 3: Getting Wet
For streaky highlights-- towel off your hair, so that it's damp, not dripping at all.
For soft highlights or all over lightness-- pat your hair with a towel, so that it's not dripping.
Remember: It's easier to get your hair drier than it is to get it wet again.