ten short questions to you as php programmer may reveal common errors you´re doing like if you secure cookie data or if you deal the comparison operators the best way. It´s short and easy to understand. Check out the comments, you´ll see that there is much more to know, but for a glance, it´s ok. Have a look at the informative phpbench as well.
I think, some of these mistakes would be made by me, but since I mostly develop for TYPO3, I´m rescued by it´s wonderful core api.