1. For bottoming: it's generally considered good manners to wash out your ass. You can just give it a good scrub in the shower, but if you want to go the extra mile, you can douche as well. I recommend doing so 1-4 hours before showtime, so it'll still be clean by the time you're getting down to business. In the shower it over the toilet, use a douche or a syringe (sans needle, of course) to gently squirt some lukewarm water up in you. You may need to lubricate the tip a bit. The water will feel very weird, but shouldn't hurt. Let it sit for a count of 10, then open the flood gates. Repeat until the water comes out clear, or you get tired to spraying water directly into your intestines.
Right after is a great time to take a shower. At this point, just standard hygiene: wash your asshole with soap and water. While you're down there, might as well get your dick and balls as well — who knows where the night will lead? And you know what? Throw in the taint too, while you're at it. A lot of dudes forget to wash that.
Now, when the moment of truth arrives, you wanna make sure both 1) your ass, and 2) his dick are lubed up with water-based lubricant (condom-safe). You're gonna need more than you think, so keep the bottle nearby. Then, I've found it helps to push just slightly; this will help relax your sphincter muscles, and hopefully he'll just pop right in. Hopefully he's also not a cunt, and will go slowly and be attentive to your reactions.
If you mean the pre-match training montage, just...I dunno, practice putting stuff up your ass. Dildos and plugs are good. Your fingers also work, and have the distinct advantage of being free.
For topping: wash your dick. The whole thing. Even under the flaps.
Once you're all clean and your partner is ready for you, make sure they're relaxed enough. I like to do this by eating their ass for a while. If their ass is kinda gross and you don't want to put your mouth on it, you can use a lubed finger or two, gently massaging the hole open. Or you can saucily suggest he shower with you, then give it a good once over with a soaped up hand, under the guise of fooling around with him.
Once he's relaxed enough to take your dick, move inside him slowly. Give him time to get used to you. You can use this time to make out, suck his nips, or whatever it is that tickles your fancy. If he's having trouble relaxing, sometimes jerking him off will help.
Sometimes the mind is willing, but the asshole is not. Assholes, both figurative and literal, cannot be reasoned with. You'll just have to 69 or something instead.
2. I personally don't, because disease transmission rates are pretty low for oral sex, and I don't blow anyone I'm not confident is clean. That being said, you can still totally get STDs from oral. Fun things like mouth herpes, genital warts in your throat, and even crabs in your eyelashes. Ick. Unless you're confident he's clean, I'd at least consider condoms.
3. That... I'm gonna defer to someone else's expertise.
