The general practice is that your skirt should be just long enough that it covers your knees when you are sitting, but needs to be “tugged” about every 5 minutes. You should practice while sitting on the couch at home to ensure this precise length.
Since this is your first date, we’ll also be nice and give real advice.
Relax, it is no big deal.
It is not awkward if there are silences for a few minutes. That happens in normal conversation with even friends.
Don’t think about whether it is going good, until you are back home.
Smile, be nice to him. He’ll be nice to you.
Be a good listener. People tend to think you are good at conversation if you listen to them.
You’re going to be fine; you will be the same good person tomorrow no matter how awkward it can be, no matter how much you dislike spending time with him, no matter how much you thought it was good but he didn’t want to date you anymore.
And most of all: give us a full report when you get home (jk).