Discuss and learn French: French vocabulary, French grammar, French culture etc.
I'd begin with reading children litterature and/or watching subtitled French shows, maybe also listening to audio books when you have the time. I'm sorry, I don't know any easy way to learn a language.
Get hold of two essentials: a French grammar book and an English/French dictionary and begin reading them. This, of course, added to children's books and films. Persistence and patience: there is no quick way. You will build your vocabulary one word at a time.
Thank you for the quick tips. I will try to apply them in my study of french language.
I actually reviewed this book a while ago, and you can find my review of Barron's Mastering French Vocabulary here.
The only thing is: to get the most out of this book, it's designed for relatively advanced students. If you're a relative beginner but looking to continue your studies for a couple of years, then it will be an excellent investment. It may not be so suitable if you just want to learn a few basic words e.g. for a holiday in France.
In answer to the general question, I would say the main thing to take into account is that there's no magic piece of snake oil that is going to miraculously make you fluent in a few days (despite books that you can buy which claim to "teach yourself French in X days/weeks" etc...).
What actual research tends to show is that in general, people need to have different experiences of vocabulary for it to really "sink in". So you should think about a combined strategy: yes, get a vocab book such as the one we've mentioned, bu ALSO try to find a bit of time each day/week to read a web page in French about a topic you're interested in, maybe think about a vocab app/application, maybe buy or print yourself some vocab flash cards (this link is to a page on the site where you can print your own for free if you don't want to buy pre-made ones), try to listen to some French songs AND study the lyrics, watch some French films with subtitles and try to see what vocab you can pick out etc. It's likely that none of these methods on their own will single-handedly be the key to learning vocab, but their combined effect is more likely to be.
Finally on this subject, in case you have an iPhone or iPad, I will shamelessly plug my own French Vocab Games app available from the site. Again, I'm not saying this is the single magic piece of snake oil, but rather it's ONE more weapon that you can add to your armory.
I use multiple methods. This (usually) keeps me from becoming bored with one of them. In no special order, I a) put verbs, or vocabulary, or phrases into an Anki flashcard database and review them frequently (Anki is freeware, though it does accept donations); b) read simple newspaper websites, such as La Montagne, noting the words that I don't know, and writing them on a piece of paper taped to my bathroom wall; c) go to one of the free language sites such as the BBCs Bitesize French; d) browse a dictionary (just eight or ten words, picked at random); e) listen to a CD of simple French songs with lyrics, reading the lyrics as they sing. I also participate in a free site called Conversation Exchange, where people who know one language and are studying another converse through email or Skype with people who know the second language and are studying the first. The conversation can be scary to do (nobody likes to think about how bad they sound) but it helps enormously.
Opera also is a help. A DVD with subtitles or a CD with a printed libretto. By it's very nature, singing slows the "conversation" down, and, although sung French can be different from spoken French in that the language needs to fit music's conventions (i.e.: often the final syllable is pronounced when sung where it wouldn't be spoken), the more deliberate expression of language in opera may be of help.