With a bit of luck, you'll find someone who's heading for a ferry (or the tunnel) who's got a ticket which, say, is for 'car +5 passengers' when there are only 1 or 2 people in the car. (Lorry drivers can usually take a passenger in their cab, without any extra fare, but it's increasingly hard to get lifts in lorries because many firms have insurance which is invalidated if anyone other than employees travel in the vehicle).
If you can't get a direct lift, make your way to Dover, and stand at the dock entrance with a 'PARIS' sign. Sooner or later, someone will pick you up.
Don't worry that you can't speak French. I've picked up hundreds of non-English speaking hitch hikers in the UK and we've always managed to communicate somehow!
These links might also help:
http://www.bbc.co.uk/dna/h2g2/A10421687
http://www.autostop.lt/faq/FAQ_F.html
NB: Carry a bright torch, with fresh batteries. I've sometimes found myself stranded in the dark at unlit, or poorly lit, junctions and my torch has saved me from sleeping by the side of the road in the rain. (i.e. use it to illuminate your sign, so that people can see you).
Also wear a high-vis vest. They don't cost much. (Tesco were recently selling them at �2 each. If they've run out, many discount stores sell them for no more than a fiver). Drivers spot someone in a high-vis vest well before someone without one. It gives them time to slow down and read your sign.
Lastly, set out early. You really need to be at the A205/A20 junction as soon as it gets light. Then, hopefully, you should be in Paris later the same day. Otherwise you might find yourself stranded overnight.
Good luck ;-)
Chris