Partial (half or less) for takeoff, full for landing. When you throttle back after takeoff is the usual time to retract flaps, and just after you throttle back and start to bleed airspeed on approach is the best time to deploy them. Try them at altitude first, to see what characteristics you get. Depending on the plane, some will pitch up a little and some will pitch down when flaps deploy. You can counter this with a elevator-to-flap mix, to help keep the proper attitude.