Overshooting turns used to be a problem for me when first riding in the early-mid 70's. I'd sometimes end up in the lane to my right, or shoulder if it was a one-laner.
Look through the turn, not directly in front of you when turning. You should be looking at where you want to end up at turn completion at the start of the turn itself.
Ditto on the above mirror statemet. Always, turn your head to check before changing lanes.
