I was wondering how to start coding a script using php, and that script will be used on many websites.
so should I start first by creating the database ? and then start creating php files that will process data from the database ?
and should I start thinking of an install wizard for this script at first, or later when I finish the project I'll create one ?
I'm really confused on how to start a project, can you please give me some advice ?

and thanks everyone :D