Prep. That region isn't known for being the most clean or the most easy to work with. Before you do anything, wash and maybe shower. Also, arm yourself with some lube.
Prep. Also, if you intend to use your hands to help get him off down by his prostate, make sure your hands are clean and manicured. No one wants wolverine messing around down there.
Finding it. If you've never done it before, you might not know how to find the prostate except on a picture. His body will actually help you out with that because his prostate will swell when he's aroused.