Always use OOP!
As lemon-tree said, use a version control system. I prefer Git, but I have experience in both and both will do the job. If there are multiple people working on this project, you will want an online git host, such as
GitHub.
Think up some
coding standards - or use someone elses, such as the
phpBB Coding Standards - and give them to your entire development team (or if it's just you, make sure you stick to them), as you want you code to be consistent.
Plan ahead! Spend a week or two writing down and thinking about what your want the final product to do, how it'll do it, etc. There's nothing worse than finishing everything, then finding you've got to make some major code edits to the core because it doesn't allow x or y.
If you've got a development team, communication is important. Use something like
IRC to discuss what you're going to do next.
As Vishal said, you can consider using a
framework. This will make life easier for you. I would recommend taking a look at
Symfony, as it leaves the developer with a lot more control.
Why not make your project support multiple databases? If you're using PDO (which you should anyway), it supports multiple databases and it is easy to switch between them. Read my PDO tutorial
here. You could also use a DBAL such as
Doctrine DBAL.