At the risk of quoting myself, you must maintain the proper engine speed and gear selection to maintain the proper road speed. Your motorcycle will have an ideal engine RPM range, where is neither too fast nor too slow for your particular motorcycle.

My scooter, of course, is 95 cubic inches engine displacement, has a six-speed transmission, pushes 72 BHP, and is the standard for excellence that Japanese bikes try to mimic.

That means, I use the transmission as follows:

0-15 MPH, 1st

15-30 MPH 2nd

30-45 MPH 3rd

45-55 MPH 4th

55-70 MPH 5th

70-120 MPH 6th (I do not drive that fast on roads where it is illegal to go that fast, but such roads really do exist, say, from Berlin to Stuttgart -- the Autobahn).

NEVER "lug" or "scream" your engine: use the proper gear ratio at all times. Unless you are driving a HD, FLHTCUI, your choices of gear ratio will be considerably different.