Take your nipples in hand and play with them as you like, whatever turns you on, and do so until you start to get hard without touching your cock. If you cannot get hard after 5 minutes of nipple play, you may lightly stroke your cock with your non-dominant hand, while you alternate pinching your nipples with your dominant hand.
Once your cock is hard, rub it back and forth with both of your hands without any lube. Rub your cock as if you are trying to start a fire by spinning a stick. Do this for 2 minutes before continuing.