Firstly be prepared as to where the turn is. Look out for signs, markings and spaces in between buildings. Remember your MSM routine (mirror, signal, maneuver).

Turning left.
Check mirrors (especially looking out for cyclists and pedestrians), position to the left, signal left, slow down and change down gears if needed (1st gear if you're turning in to a small or uphill road,  otherwise 2nd) making sure that you release the clutch before you turn. Although you have priority always be ready for what might be in the road that you're turning in to such as pedestrians crossing, parked cars or a traffic jam.
Use your 'pull-push' method of steering, following the corner of the turn keeping about a metre from the kerb.

Crossing arms when steering, steering wide, not using mirrors properly, signalling late/early.