My answer isn’t going to be much fun, but I think it’s important for a first time.

First things first. Consent: explicit and enthusiastic, continuous and revocable, free and informed. It’s an ethical question and that’s the only justification needed. I’d still add that it’s the bare minimum if you don’t want to screw up your relationship, and if you want penetration to go well because she’s sufficiently lubricated.

Secondly, think about birth control (pill, condoms, IUD.) and STI prevention (condoms). Yes, even if you’re both virgins. In particular, the papillomavirus isn’t only transmitted by sex, it doesn’t have any obvious symptoms, but it can cause uterine cancer. So use condoms and get tested. And with condoms, a little extra lube is always a good thing.

Finally, while we’re on the subject of no-fun advices, communication is key. Sex is a sensual activity, like music or cooking, which means that everyone has their own preference and desires at the time. It depends on each person’s nervous system, what they saw and want to try, what they’ve already done and want to do again, and so on. So, there’s no magic formula that always works for everybody, you have to communicate to know what to do. It can be words, it can be being attentive to their reactions, it can be letting yourself be guided by the hand, it can be a bit of all that.

Finally, don’t feel limited to the sexual script you saw everywhere (I mean, on youporn). It doesn’t have to be step 1: kisses, step 2: boobs, step 3; masturbation/oral, step 4: penetration. Take your time. Penetration is not the ultimate achievement.

P.S. to answer your question: missionary is one of the easiest position, you can kiss and you get feedback from each other.

P.P.S cut your finger nails