http://www.flyingmag.com/technique/tip-week/lining

This is pretty basic stuff, but you need to be sure that the controller calls your N-number with the instructions “line up and wait” or “cleared for takeoff.” Make sure that the runway you’re taxiing onto is the one you’re cleared to enter by looking at the red sign at the hold-short line or, if you can see them, the white markers on the pavement. You may think this is obvious, but there have been highly publicized accidents caused by pilots departing from the wrong runway, so a final check to make sure you are taxiing onto the runway you think you are is well worth it.