Too hard a prsure on the pedal might be the major problem.
Though going beyond that, don't grease the rotor itself, you only grease the back of the pad that touches the piston, to stop the vibration of the pad (if you don;t know) if you do grease the rotor it will make it harder to stop and you'll get the squeeling.
Another problem you can get is brake dust or brake pad dust, if you have to much it will cause the squeeling, use a spray brake rotor cleaner so you don't have to take the caliper completely off the rotor.
Anthor would be to change the pads, probbly the wrong type of pads for your driving style as top notch racing pads will squeel as they arn't up to the correct temp etc, so dropping back to more street type or semi race type pads would be better.
I've read that the endless g spec are good for street and race track, but they really dust up.
Another thing to check is the brake ratio as too much presure could be on the front brakes might need to change that as well.