Ok, I'm pretty new to cycling and am wondering if there is some lack of technique I can blame this on. When I pedal at a higher cadence (85+) and am pushing a low (easy gear) I feel like I am overspinning and bouncing from side to side on my saddle - ie. I have little control of my legs. My solution has been to up a gear to increase the resisitance but I think maybe this is the wrong thing to do as I am trying to teach myself to ride with a higher cadence and after a while in the harder gear my legs get pretty tired.

I have been doing some one leg drills on the trainer and sometimes find (particularly at the end of the session or if I'm tired) that the top (10 - 1 o'clock position) of the pedal action on both legs is not very smooth. It feels like maybe I start the down stroke too early or something like that as my foot sort of clicks over at the top and is not a smooth action like the rest oof the cycle.

I am riding clipless by the way. Is this bouncing and overspinning a beginner problem or does everyone experience it? If it can be fixed, is it something I can improve by doing certain drills or will it just take time?