1.Arousal from ass and clit play and licking and other foreplay.
2. Lube, Lube, then a little more lube. Warm it up. Waterbased, may want to add a little warm water to make it more viscous if too thick.
3. Reasonable size butt plug small penus to medium at widest point. Have a toy with a little depth. Chrome vibrators are the best.
4. Relax and let you partner insert with you guiding. Completely go limp. You not him! Spend a lot of time with the toy or plug/vib slowly building speed and depth till you are comfortable and confident in you and your partner.
5. Main event. Repeat steps 2-4 with the real thing.
Communicate pain or wish to slow down before you think you might need it. Early detection is the key
. If you clinch up it is usually game over.
Or just slam it in hard and dry. Your call!