Squeeze the juice. If you’re looking for overall color, after cutting the lemons in half, squeeze the juice out and into a cup.
Grab a tool of your choice. This can be a hairbrush, a wide-tooth comb, a toothbrush, a mascara wand (make sure it’s clean, obviously). Dip it into the juice. Apply it on your hair until all your hair is soaked with lemon juice.
Lastly, find some sun! The juice will only work with sunshine, so get out there and make sure your hair gets some sun. The longer your hair is in the sun, the lighter it will get, although 20 minutes is more than enough to get a little bit of difference.