Very hard to acheive a mind/muscle connection for most people when training rear delts.
Envision two pads up against the back of your elbows,then push the "pads" back as opposed to pulling the weight..............real ly helps to isolate the area no matter what exercise you are using.
For lateral head of delts,try doing strict laterals,arms slightly bent at the elbow to take stress offf the joint..........now instead of doing a lateral raise,do the lkateral raise behind your back...............real fucking good old school shit that not many know about.
Also,learn to "pull" with the side head as opposed to just swinging or raising and lowring.