Go slow and use plenty of lube. And like one respondent said, clean out with a warm water enema. Don't use the saline ones like fleet's as these could cause cramps. And always maintain control of the insertion. I hooked up with a guy who took me so fast I wasn't able to relax enough. Then he practically pummeled me for the next ten minutes or so until he orgasmed. I was sore for a week afterwards.
Bottom line is take what you can handle at the pace you can handle.
Honestly, take it easy. I went very slow with my gf. We didn't rush. Use lots of lube and if you want to clean yourself out with an enema. You really shouldn't need coaching. Just take it slow. You can also use vaginal pleasure at the same time. It may help mask some of the first time pain. But again take it slow and make every moment and intimate one. It will take many times for it to be easier to do. Until that time go easy!
There are definite issues that can occur. First, always practice safe sex and absolutely with anal. There are plenty of diseases associated here.
Being rough will do damage. I hear cases often about damaged prostate and rips that never fully heal. I would suggest if your partner is not gentle move on.