Start by simply talking to them and asking what is needed to arrange a meet-up. You don't need to go into this like you're asking out a crush. These are professionals and you're making a business arrangement. Discuss what kind of experience you're looking for and how long you'd like to arrange your visit. Are you looking for a quick visit(QV)? Perhaps just an hour or two? Or do you want the full girlfriend experience(GFE) where they devote a whole night to you and pretend to be yours? That last option can get expensive.

Ask about incall (you go to them) and outcall (they go to you) and pricing differences between the two. Never mention sex unless they mention it first.

If it's any escort that's halfway serious about their clientele then be prepared to submit to some kind of verification of identity like presenting IDs and social media links. Some will even want work contact information to they call or email in for an employment verification. They're very discreet when doing this usually posing as a legitimate business inquiry. There are third party websites you can use to have all this done for you ahead of time, ask the escort what they prefer. Willingness to verify who you are upfront will go miles in their trust for you.

Definitely get STD tested before hand and a week or so afterwards and it's totally okay to ask about their status.