These have been touched on already, but if you have a good understanding of them you're well on the way to becoming a competent sailor.
When the sails are set correctly, not only is the boat generating maximum power and thus speed, but also your ability to control the boat with the sails is enhanced. In general you can say:-
Close hauled - sails hauled in as far as possible,
Running - sails let out as far as possible
Reaching - inbetween.
Watch the front of the sail. If it flaps or "goes backwards" then you the sail is too far out. Too far in is a little more difficult to spot, so keep looking for the too far out spot - let the sail out a fraction and pull it in a fraction when it gets to too far...
The centreboard also needs to be adjusted on different points of sailing more maximum control and efficiency. All the way down close hauled, partway on reaches and most of the way up when running (always keep some down - it aids control.
Its too often underestimated how important balance is. A boat will sail unbalanced and heeling over, it may look spectacular, but in dinghies its slow and difficult to control. You also use the balance of the boat to aid the steering.
Trim is the fore and aft balance - whether the front or back is deeper in the water. The force of the wind on the sails alters the trim of the boat, pushing the stern down when close hauled and the bow down when reaching. Basically you aim to keep the boat level, so to counteract the effect of the sails you need to move slightly forward when beating and backwards when running. The effect is usually subtle and in most boats you may not need to move very far.
When going from A to B, don't travel via C. Diversions are slow. You should aim to sail the boat smoothly and on a steady course.