There is no magic recipe. The key things are to take it slow,
keep it short, relax and do not plan it. Tension, stress or
apprehension can cause muscle to tense up, which is a big problem.
Make sure to spend a LOT of time on foreplay.
PS Never make the decision to have sex for the first time while
making out or fooling around. That should always be a 'clearheaded'
decision for both of you. However, after the decision is made just
let it happen, you will know when...