I ride for fitness and fun and the occasional sprint tri. You will get great responses from the hammerheads on here but I was always told to start with a high cadence (rpm) and low resistance and the speed would come. My friend who is training for an ironman duathlon just hired a trainer for her cycling. She was given a set time to ride in the small chain ring and keep a cadence between 80 to 90 rpm. The time on the bike increases every week and the speed for now is not a concern. Thats just my 2 cents. I know for me it has worked.