Rule 1: Be PREPARED! Always bring some papers to feed the ever hungry French system

Before you come to France!

French bureaucracy loves papers, any size color and detail.
So before moving to France (and afterwords) make sure you keep any (and I DO mean any) official paper you received since you were born.
These papers often depending on quantity rather then quality, and they will serve you for many reasons including but not limited for your: National Insurance, Unemployment benefits, paid training*, CAF (government aid for paying rent) or even getting the land-lord to rent you the flat.

I do mean every paper but I can give you some examples:
Birth certificate.
Payslips (all of them).
Work contracts.
Renting contracts.
Any kind of proof for unemployment benefits.
Your ID, Driving license, Passport. (Preferably at least two forms of Identification).
and your bank statement.

Trust me you will use most if not all of them.
For my social security number they even asked me to write the current date in the side of my birth certificate and send them a copy of it.

If your papers are in your native language note that you might need an official translation service. If you have a friend who is a lawyer it would be wise to consult with him for free.
Although in France there is assistance for translating papers from most languages and it should cost around 50 euros, I will post more details in the near future.

*Yes you can actually get paid to study French if you are under 26! I will post more details about it in the near future.
If you are above 26 you can still get free French lessons and certificates.
Paid training are not limited to French they also include a variety of practical professions such as cooking, plumbing, car mechanics courses, computer orientation classes and many more.