Kief screens are excellent ways to collect the highly potent kief crystals that fall off your buds. The best way to use a kief screen is to get yourself a good 4 piece weed grinder. The first two pieces of a 4 piece grinder crush the buds releasing kief along with the ground buds down onto the third piece, which is the actual kief screen. The screen then catches the ground buds but allows the kief crystals to pass through into the forth piece, or the kief catcher. Over time the crystals build up and you can collect them.
For the average person, a grinder with kief screen is perfect for getting kief. Using the screen with this method will insure that only the pollen is collected and not any shake from the buds. There may be quicker methods out there, but using a weed grinder is the most tried and true way to get quality kief, where the other methods generally result in a mix of kief and bud. A technique for speeding up the process with a grinder is to shake the grinder once the buds have been ground.