Form verification

I'm trying to come up with a general solution for validating data in forms as far as empty fields. I've considered doing javascript, but would prefer to do the method where the page shows the previous form, with notes near fields that need to be filled out properly. My problem is I am trying to come up with a solution that will work in several forms so I don't have to modify every form I create. Any suggestions plus example code would be greatly appreciated. Thanks -Justin