Not only is a good, thorough wash-out vital, but you need to allow yourself time to "dry out": trust me on this. As much as I love fucking ass (and I do so love fucking ass), all it takes is one last squirt or leak and I'm done.
As far as foreplay goes, I'd say the longer the better, especially for a newbie. By longer I mean 30-45 minutes at least. Getting yourself ready is nothing to rush into. Analingus (anal/oral contact) is a requirement.
Not every bottom enjoys fingering as part of the opening-up process, no matter how gentle the top can try and be. You might have better luck with a soft, very pliable dildo: it's not so insistent as a finger or two (or three or four
)
I have to admit that I've only had vaginal sex with women, never anal. But I have 30+ years experience fucking men, and I've noticed that as many bottoms respond to the pleasure they're deriving with their ass alone as with their ass and penis in combination: they focus on their ass at the exclusion of their penis.
You might be similarly wired, or maybe not. But I would like to at least suggest that you not focus unduly on your clitoris when getting fucked in the ass, at least not at first. Men have "assgasms", and so might you.
I'll also suggest that some lubes are better for anal sex than others. Superpremium lubes are silicone based, like Gun Oil or Eros. They are silky and smooth and thicker than baby oil but not as thick as KY. They also are the only condom-friendly lube that stays wet indefinitely. But it is extremely expensive.
If condoms are not an issue for you, then I'd recommend Elbow Grease, which is odorless, stays wet forever, and has the consistency of cold cream. It is by far my preferred lube.
Crisco, BTW, is flawless and inexpensive. But don't keep an open can in the nightstand for more than a week or so. It can attract bacteria.
Good luck and have fun.