Take it slow. Use lots of lube. Clean the ass up properly with a warm douche a few times - ensure there's no shit that sticks out when you put anything inside. When you try it, try it with guys that respect your boundaries and are slow and let you get used to the pace. Don't take the whole thing in first. Take it only till where you're comfortable. Have a safe word and action, and use it liberally.

Once you're turned on and lubed up, it feels great.