dicksewerrat and Ron are both right, to a point. While size and slope are generally not that important in French drain design, you must pay careful attention to the gradation of the rock/sand that is around your drain pipe and the gradation of the natural soil that you are draining.
If you can avoid using filter fabric the French drain will perform better for a longer period of time. Ideally you want to use a sand/rock that will serve as a filter for the natural soil that you are draining. The permeability of the sand/rock should be at least double that of the natural soil. Second the holes in the pipe must be small enough not to allow the sand/rock to pass into the pipe.
With all of that said, yes you can just use a non-woven filter fabric between the natural soil and the sand/rock and between the sand/rock and the pipe. Good Luck.