1. First, remove the rubber piece that comes with your turntable and replace it with a slipmat, this allows the record to move more freely when the platter is spinning. If you do not have slipmats they can be purchased cheaply at most record stores and DJ equipment shops (see the Links section for online DJ stores).
2. Listen to the song through your headphones only (so that the song you're cueing can't be heard on the dance floor). With the start/stop button on the turntable on START, place the needle at the start of the record (or near the note you want to use) and move the record with your hand so that the needle is located exactly on the note you want to use.
3. Placing the tip of your index, middle and ring fingers on the record, move your hand back-and-forth with fluid motions so that you can repeatedly hear the note you want to scratch in the headphones. The slipmat should allow the platter to continue rotating as you hold the record
As long as the turntable is direct drive, you don't have to worry about damaging the drive when you cue in this manner. In contrast, the belt on a belt driven turntable may eventually break because the belt builds friction and stretches over time, so dont go doing this too often on your friends belt drives!