1. Run the affected area under cool water for about 10 minutes to stop the burning process.
2. Pat dry (no rubbing) with a clean cloth.
3. Apply a soothing ointment (burn gel if you have it) and a loose bandage (do not wrap burns tightly).
4. Take an ibuprofen.
(Disclaimer: Obviously I have what amounts to zero medical knowledge; if you’ve suffered anything but the most minor burn – that is, if you see blistering or charring, or if the burn is larger than a quarter – please consult an actual medical professional.)