It sounds like you should just have a discussion about sex to set expectations. You can start with basic questions about how soon that may or may not happen, etc.
This is a completely normal and reasonable discussion to have when getting together with someone, and segues nicely into discussing specifics about what they like and what they want (or don't) in a relationship sexually and otherwise.
So just have this discussion that you should have anyway, which often has an expected degree of awkwardness, but can be used to set expectations about any aspect of your relationship. At that point, depending on your partner, you could ask how much experience they've had with sex, likes and dislikes, etc.
If you ask about their preferences with specific acts, you may get an answer that tells you what to expect regarding their physical sex characteristics, which seems like the main thing you don't want to be surprised by (it could certainly be awkward to expect one body part but get another, even if you're open to it going either way--if that made you hesitate, it could make them feel unwanted, so better to get it out of the way instead of being surprised in the moment).
Edit: Also in the vein of talking about sex and to offer a more concrete example: prior to actually having sex, you could talk about sexual fantasy. You can ask what they think about that turns them on, and if the right situation arises, you could ask for them to describe what they'd like you to do to them, or ask them to describe what you'd see if they undressed (possibly over the phone. Exactly how to approach it depends on how shy or how direct this person is, which may be influenced by culture).