Raquel,

You will need the following:

Birth certificate not older than 21 days prior to your marriage
If you have been previously married then your marriage certificate and divorce papers
Certificate of No Impediment (CONI) available from the British Home office
These all need translating into Arabic/French and can be done here in Tunisia very cheaply
You and your fiance must have blood tests but they must be done here - they take only minutes and is cheap
Passport

There is loads of information on: www.tunisia.com mainly for British and Irish women so you will find lots there to help you.

Good luck