Besides finding a place to stay you will also need to be reachable.
The easiest way is to buy a SIM card. It costs around 20 euros and if you already have a cellphone this is the fastest way to get a French phone number. The main French mobile phone lines are Orange, SFR [Vodafone partner] and Bouygues Telecom.
A more long-term option is to subscribe for amonthly plan (for 1 or 2 years). This offers better calling options, but in order to subscribe you need to have a FRENCH BANK ACCOUNT, and some proof of Paris location or payed bills. So this can be a bit complicated.