Don't think too much. No, seriously, kill like the majority of your thoughts and try to wrap yourself up in the moment, and not about what you should do. There is no standard of what is expected other than to be yourself. Besides, even if you did something highly embarrassing, it'll likely break some tension. Trust me, the other person is also walking on egg shells, it'll also allow you to be slightly more comfortable. Also make sure they know afterwards that you enjoyed the time. You'd be surprised how much the other person will think about whether you did or not. Don't let them fall asleep torturing their mind.