C'est parti for informal French!

Here are a few phrases and words that can make you feel awkward if you don't know their meanings.

Ç'est parti ! - Here we go / we're off !

Ça vaut le coup - It's worth it
On voit que dalle - You can't see anything
Ça va être chaud ! - It's going to be tough!
Fais voir - Show me / Let me see

débarquer - to arrive without notice
bosser - to work
bouffer - to eat
bourrer - to stuff, cram
être à la bourre - to be in a hurry 
être à mourir d'ennui - to be very boring
faire gaffe - be careful, pay attention
filer à l'anglaise - to leave without saying goodbye / to take a French leave
flipper - to go crazy, flip out
louper - to miss
piquer - to steal

If you can't remember the name of a thing, you can use ce truc, ce machin, ce bidule or cet engin similarly to the English thingy, thingamajig, whatchamacallit, etc.

What's-his-name is Monsieur Untel and what's-her-name is Madame Unetelle. You can also use Machin but it has a more derogative meaning, as if you are saying the person is merely an object.