To gravity bleed, do not pump the pedal before bleeding. Remove the master cylinder cover, fill to proper level with the proper type of brake fluid and leave the cover off. Open one bleeder valve. New or rebuilt calipers may take a minute or two before the fluid starts to flow out of the bleeder valve. Allow the fluid to flow until no bubbles come out of the bleeder, usually takes another minute or so. Close the bleeder and repeat the process on the other side and then close the bleeder. Make sure to keep the master cylinder full at all times during the process. After the gravity bleed is done, have an assistant pump the pedal slowly a couple of times until the pedal is firm, then hold constant pressure. While pressure is applied to the pedal, slowly open the bleeder, then close it. Repeat until no bubbles appear when opening the bleeder. Repeat on the other side, fill and cover the master cylinder....done.
If the vehicle has ABS, make absolutely sure the master cylinder does not run dry. If it does, it will require an ABS capable scan tool to manually open the solenoids in the ABS unit to bleed the system.