Know 'the lay of the land.' Single most important thing for a lover...especially a beginner. If you're not sure where the clit is, ask for help. We'll be happy to assist you.
And enthusiasm is good, but early in a relationship it's important to keep your wits about you during sex - stay aware. This is largely how you learn what your partner likes and doesn't like. Very important.
An open mind is also very helpful.