For a start you must have a driving license, issued at least one year ago.
Then, if you’re traveling abroad, you must have a passport or a valid stay visa. In some cases you’ll have to make a deposit to cover eventual damages, theft, loss of documents or keys. If the car is returned in good condition you will be refunded.
Most of the rent a car services fees are calculated in euros, but cash payments are charged according to the official currency exchange rates on that particular day. Upon delivery, the client will receive a full tank car that he/she will have to return in the same condition or will have to pay additional fees. The company is in charge of oil and general vehicle good functioning. In case the customer makes an oil refill, they will be reimbursed according to the invoice.
Usually the rented cars are insured for third party liabilities. Damages caused by the client will be entirely his responsibility.
These are the most important things you’ve got have in mind when you rent a car. You must have valid IDs, be prepared to pay the fuel expense, and be careful. As you can see, it’s nothing different from being just another responsible driver, so you shouldn’t worry too excessively.