Practice practice practice. That’s the best thing you can do to start. Use a dildo or something to practice with. By doing this first, you can quickly figure out what you like and what you don’t, how much lube is necessary, and what positions feel best
It’s not recommended to just jump into it with no real concept about what you’re getting into. Like the posts above suggested, use more lube than what you think you need. Sex should feel good, it shouldn’t feel painful. Communication is key. If something doesn’t feel right make sure you express that. Sometimes it takes a few tries to get it to feel just right for you. Like the previous post says, YOU are in control of how things play out. If your top gets annoyed with you then tell them the door is right there.
In terms of cleanliness, I’m pretty picky and prefer to be as clean as possible but I refuse to douche. It just scares me lol. So a clean diet high in fibre and a wash in the shower has worked best for me. But everyone is different! Good luck