The most common reason is over-torqued or unevenly torqued lug nut(s).  Making sure you use a proper torque wrench with all four wheels on the ground is the best approach.  The use of an impact wrench is NOT recommended.  Your vehicles manual will indicate the proper torque rating (ft-lbs). After you tighten one lug nut, the next one you tighten should be diagonal from it.

Another primary cause of warping is caused by excessive heat.  This is why choosing the best compound and running proper brake fluid is extremely important.

Riding the brakes lightly will generate a great amount of heat and is not the proper way to apply the brakes on a vehicle.  The proper way is to apply the brakes strongly for a shorter distance and then completely release the brakes.  This will allow the brakes to cool before the next application.  Racing brake pad compounds are engineered to properly handle this type of extremely high temperatures.

Not all pedal pulsation is due to warped discs. Brake pad material operating outside of its designed temperature range can leave a thicker than normal deposit in one area of the disc surface, creating a “warped” disc feeling for the driver.