With due respect to the above write-up by KayTay, I would disagree. The following is what you need to know to have a decent conversation in French.
In terms of verbs you need to know:
Verb tenses you don't need to know at the begining are
Thereafter you should consider, as KayTay recommends
You do not need to learn the subjunctive in all its hideous deformed mutated mish-mashed forms. In fact the average French speaker only knows a few common cases of its use, and in the inner city it has disappeared entirely. You do need to know how to avoid it though, e.g. devoir instead of falloir, using de instead of que etc.
Past Historic is mainly used in books, you will virtually never encounter it in conversation (unless you talk with exceptionally verbose, grammatical people, think 60-something English lecturers with PhDs). Like the subjunctive an awful lot of it is irregular.
You need to get a good hang of reflexive verbs, particularly how they relate with pronouns. You should also get a good idea of the stuff in the last section described above (though note that for most French people the "interrogative" is basically just the standard tense with the voice raised, Peut-Je and the like are English-isms).
Once that's done build up a basic vocabulary and you should be able to hold a decent conversation with someone from France.
As regards French grammar itself, in my experience it is harder and more convoluted than it initially looks, and beyond a certain level, depressingly irregular.
If you're interested in learning more, this site is a good place to start, and surprisingly comprehensive:
http://www.languageguide.org/francais/grammar/index.html