Woof!! Great that you're planning for this and thinking ahead. Sounds like a hot and piggy night. A few tips...
1. Take it slow and communicate with your friend clearly if something feels off and he needs to stop
2. Lube. So much lube. Get an injector if possible and use something like X Lube. Put down towels or puppy pads, and have paper towels available to wipe. Make sure your bud trims his nails and washes his hands thoroughly and/or wears gloves.
3. Set the scene. Music, lighting, no distractions to help you and your top relax and focus.
4. Breathing. Deep breaths help your muscles relax. Time them with your top to help him stretch you further.
5. Positioning. Your hole, hips, spine need to be aligned, so work with your bud to ensure you're comfortable and positioned correctly.
6. Don't be afraid to take breaks. Put in a plug to maintain the stretch. Your bud will also need a break - it can be exhausting opening up a hot hole.
Enjoy... after you take your first fist, you will want more. And more. And more.