A few suggestions, since I’ve looked into this a few times. First, it really shouldn’t hurt the first time if you do it correctly. Unfortunately, going right at it is not ‘correctly’ (YMMV, naturally, depending on your kinks, but I’m going to assume pain’s not a goal here). I will definitely second @partyrock‘s and @Thammuz‘s suggestions of plugs, that’s the best idea. I would suggest a smallish and medium flared one, and practice with those. Do it when you’re relaxed and with lots of lube, and you shouldn’t have any pain. If you do have any pain, stop and use more lube and possibly check the angle. Within a bit you should be comfortable enough with the level of stretching that you can have anal sex again with your partner with no trouble.
Also, though again YMMV, i wouldn’t personally suggest poppers and certainly not pot, and that’s with legality issues aside. Poppers may be safer then I expect, but in general messing with your body to have anal sex is usually not a great idea. It’s a rather delicate area and things that mess with muscle control are usually not good. And pot doubly so, because it’s going to mess with your head and make it harder to deal if something goes wrong. You may not realize you’re in pain, or simply ignore discomfort, etc, that may tip you off otherwise. So, personally, I wouldn’t suggest it. But again, YMMV.
As far as position, I’ve done it in missionary and that worked quite well. I haven’t tried doggy yet so I can’t comment, but missionary is a good one, though a pillow under your butt may help with the angle, since it’s a bit different, naturally.
@Hypocrisy_Central is there much of a difference in advice? Assuming I’m even understanding your slang, which I may not be.