I'll give you a few tips that helped me:
1. Do not eat before you bottom.
2. Douche your hole - using an enema or another calonic aid.
3. Make sure your top starts you off by penetrating you slowly first; going too fast might irritate your anus or make you uncomfortable.
4. Have both of you discussed what turns the two of you on? Maybe you can dress up how he likes, buy the sex toys he loves, etc. - do whatever makes both of you more present & turned on.