I think the two most common mistakes with dropshotting are casting out too far and overdoing the movement. If you want to cast to far banks or features you're better off using a jig head or spinning. With dropshotting you're better off dropping the lure at or near your feet by a feature. For the movement, remember it's a finesse technique. Try to keep the weight still on the bottom and then impart very very small movements to the rod tip.
Other tips:
- use smaller hooks and lures than advertised in most drop shot ads. Start with a size 8 or 10 and a 4cm lure, not those 10cm jobs with size 2 hook.
- try different lure shapes and colours, see what works
- keep trying. I find it takes a while to get "in the zone"
- when your lure is in the water try and "feel" what is going on under the surface
- as with all perch fishing look for snags, cover, features, slack. You can't catch what ain't there