Use OOP correctly. Don't turn OOP into the point of your programming style on any project. Don't use it at all when it's not appropriate. When you don't use

Use OOP correctly. Don't turn OOP into the point of your programming style on any project. Don't use it at all when it's not appropriate. When you don't use OOP, make sure you're using the right thing for the problem domain at hand. When you use something programming paradigm other than OOP, make sure you use that correctly, too.