I think most people can count out seconds, which is 60 cadence. This is about what most new riders use, but it uses too much muscle strength and is tiring. A 90 cadence is what I average. To get 90 cadence increase that tempo so you get 3 beats for every 2 seconds which is easy to do sounding it out with a watch, using 1,2,3, 1,2,3... a medium/slow "waltz" tempo, but instead of counting in your head let your legs do the counting.