Let's be honest; the process of learning French takes years, but it can be considerably speeded up by spending as much time in France as possible, listening to the spoken language (as well as trying it for yourself).
But you must realise that no matter how much you achieve over the years, the French will always detect something in your speech that gives you away. I doubt you'll ever really get away with trying to convince French people that you are one of them. So, satisfy yourself with being French in spirit, and offering the best possible rendition of what it is you want so say...make the effort and the French will appreciate it.
To help you on your way, here is a list of some common expressions. Listen for them; use them whenever you can, you'll be surprised how nicely they fit in with what you already know. The translations given are the most common; as you practice your French, you'll come across many variant meanings, and different occasions when the same expression means different things according to your social relationship with the group you're in...but now we're getting into slang (mots argots)...
à cause de because of, due to
à la fois at the same time
à la vôtre! cheers! - also santé
allez-y! Go (as in when you are giving way to someone)
allons-y! let's go!
à mon avis in my opinion
à peine hardly
à peu près about, approximately, nearly
a priori at first glance, in principle
à tes souhaits! Bless you! - as when someone sneezes, but note you can only use 'tes' if the someone who sneezed is someone you are on 'tutoyer' terms with; if it's, perhaps, someone in a group that you don't know very well, you can still bless them, but say 'à vos souhaites!' instead.
au cas où just in case
au contraire on the contrary
au fait by the way
au fur et à mesure as, while, i.e. at the same time
au lieu de instead of, rather than
avoir l'air (de) to look (like)
bien entendu of course, obviously
bien sûr of course
à bientôt see you soon
Bon anniversaire! Happy birthday!
Bon appétit! Enjoy your meal!
bon marché inexpensive, cheap
ça m'est égal it's all the same to me
ça ne fait rien never mind, it doesn't matter
ça va? how's it going? [In response, this means 'Fine!']
ça vaut le coup it's worth it
c'est it is; c'était it was
c'est-à-dire that is, i.e., I mean
ce n'est pas grave it doesn't matter, no problem
un coup de fil phone call
un coup d'œil glance, quick look
d'ailleurs moreover, besides
du coup as a result
du jour au lendemain overnight
du tout not/none at all
en effet indeed, that's right
en fait in fact
enfin well, I mean
en retard late
être en train de to be in the process of doing something
faire cadeau to give (something)
grâce à thanks to
il(s) est (sont) it is/they are
il faut [que] it's necessary [that]
il y a there is, there are
J'arrive! I'm on my way!
Je n'y peux rien There's nothing I can do about it. Or, on n'y peut rien - there's nothing anyone can do about it
Je n'y suis pour rien It's got nothing to do with me
je t'aime I love you
métro, boulot, dodo [slang expression for] the rat race; it means underground train, work, sleep
n'importe quoi whatever
oh là là oh dear, oh no
on ne sait jamais you never know
on peut se tutoyer? can we use tu?
On y va? Shall we go? Ready?
par contre whereas, on the other hand
pas du tout not at all
pas mal not bad, quite a bit
pas terrible not that great, nothing special
plus ça change... the more things change...
prendre une décision to make a decision
quand même anyway, really, finally
quoi de mieux? what could be better?
rien à voir nothing to do with
si tu veux if you will
si vous voulez if you wish/will
tant mieux it's just as well, even better
tant pis oh well, too bad, tough
tout à coup all of a sudden
tout à fait absolutely, exactly
tout à l'heure in a moment
tout de suite right away, immediately
tout d'un coup all at once
valoir le coup to be worth it
voilà there is, that's it