Starting at the outer end of the handlebar, wrap the tape clockwise around the left handlebar and counterclockwise around the right handlebar. This allows the tape to self-tighten as the rider pulls back on the handles.
If the tape has adhesive backing, overlap the tape so that the adhesive touches both the tape and bar in each segment. Keep enough tension on the tape while wrapping so that it isn't loose or sloppy in the corners, but don't pull too hard or the tape might break. Use care when passing the brake levers, pulling the housing back so that it's possible to tape around the lever without it becoming too bulky. Use PVC or electrical tape at the end of the wrap to finish.