Study the basics of French grammar thoroughly --- make sure you understand the rules, even if you don't know any words yet. You can imagine how much more difficult English would be to learn if you thought that "talk" and "talking" were completely different words instead of just two forms of the same one. Avoid making the same mistake in French by starting with the fundamentals of verb conjugation and tense, word order and gender, and any time you come across something that doesn't seem to make sense, study the rules until it does; take as little as possible for granted.
Practice the gender of nouns; learn whether they are considered "masculine" or "feminine," a somewhat arbitrary name that frequently has little to do with the word itself. There are many rules you can use to your advantage --- for example, nouns ending in "-ette" are feminine --- but for others, you may have to commit the gender to memory by rote. Gender is fundamental to the language, and you need to make thinking about noun gender second-nature.
Make some flash cards that help you to remember what you've learned so far, and practice with them until you can immediately recall the gender of a noun and the way a verb is conjugated. Even if your vocabulary starts out small, it will grow larger quickly. Keep adding flash cards, and practice with them daily.
Start keeping a journal early on in your French studies, using your flash cards and a dictionary to broaden your vocabulary. Even if what you record is simple at first, it will help get you in the mindset of thinking and writing in French. Language is one area in which "learning by doing" is a valuable skill.
Purchase some French versions of English-language movies and television shows that you've watched before. At first, turn subtitling on so you can get an on-the-fly translation of what's being said. As you get better at the French language, turn the subtitles off and see how much of what's going on you can pick up from the French you know and what you remember from the movie.
Start reading books in French about topics that you're interested in or have a familiarity with. Words that might otherwise seem mysterious can practically translate themselves through context if you know the material already. Plus, because it's a subject you're interested in, you'll have a motivation to keep reading beyond just learning French.
Find a French pen pal or someone with whom you can correspond over email or, preferably, a voice-over-IP service like Skype. Look for someone whose interests --- like sports, music, or technology --- you share, so you have something to talk about and it doesn't just seem like a tutoring session.