Tips: relax, breathe, plenty of lube, go slow and did I mention relax. If you just bend over, slap some lube on your hole and try to shove it in, it's NOT going to be pleasurable. If you watch any gay porn movie you'll see that most times the top spends a lot of time getting the bottom ready through rimming and fingering, but also rubbing his back, torso, legs and a lot of kissing. Then, when he knows his bottom is ready, he lubes up and slides gently in especially if he knows the bottom is new to it.
The toughest part is getting the head of the cock past the anus and into the rectum. There's usually a discernible "pop" once that happens. Again, the key is to relax, breathe and enjoy it slowly.