Beating man coverage has to start with the release, specifically against press man. 1 step, 2 step, 3 step, foot fire...or a combination of any of those to "move" the defender without the receiver really having/needing to deviate from his path. Teaching points need to address hands as well as footwork.
It's also important, if the defender isn't pressing, that you attack the leverage of the defender. Often times a defender will play inside leverage to discourage an inside release...that needs to be attacked, going back to the point made above about moving the defender without the WR having to deviate from his path. Certain coverages are going to dictate the leverage of the defender...that goes back to the point a previous poster made about recognition. Rarely are you going to see a man defender with outside and off leverage...if that guy is in man the slant is going to be a gimme but the WR is going to take a lick from the inside defender (SS or LB, whoever is allowing CB to play that leverage).
Once you get the release you need to stack the DB as soon as possible (i.e. get on top of him), especially if you've got a route that doesn't necessarily break back to the QB. Getting on top of the DB ensures you've still got full mobility once you make your cut.
Assuming the DB stays in phase, the next step is the break point. Speed cuts are the cuts we probably all did as a kid...put one diagonal foot in the ground and make your break. But on any route longer than 8-10 yards its going to make a speed cut susceptible to an undercut by an off-man DB, so on sharp inward or outward breaking routes receivers need to drum the feet (don't forget to coach the hands!) and really accelerate out of the break (eyes over knees).
If the DB stays on top, the receiver also always needs to keep his body between the QB and the DB (box him out, so to speak). Running a comeback? Work back down the vertical stem and allow the QB to throw it to the sideline so the DB has to go through you to get to the ball. Running a 10 yard out? Break point needs to be at 12-14 so you give yourself some room to work back towards your QB and disallow the undercut.
For the athletically inferior athlete, routes that are built more for speed aren't going to be very beneficial. If they are crossing routes, as a receiver you have to try to keep the defender on your upfield hip...if he gets underneath (especially with deep help) the throw is going to have to be something special to be completed. And for cripes sake be a hand-catcher! Get out the tennis ball machine and catch a ton of balls. Write numbers on every football the WR's catch in practice and make them yell out the number when they make catches to ensure concentration all the way through the catch process.
Sorry fellas...first post got a little wordy. Lurking for a while, finally decided to get involved!