I'll add some and reiterate some key points.

First - make sure that the sheaves in the mast, top and bottom, are in good shape. On the H-18 they don't have any bearings in them and they wear. Once they wear it's very tough to raise and lower the sail - the sheaves stop turning and it's all friction then. Check them at the beginning of each season, more often if you sail alot, and buy a few extra to have some spares in your box. Make sure that your halyard is not too thick - since it can be a pain on the hands, sometimes folks go to a heavier line, but heavier line will bind in the sheaves. The knot for the halyard on the ring needs to as compact as possible, otherwise it will interfere with the operation of the hook. I use two half hitches cinched up against the ring. As pointed out previously - when you hook the ring to the sail, make sure the bulky part of the knot is to the side opposite of the hook on your mast, meaning it should be to port - again, this it to keep the knot from interfering with the hook (sounds trivial but it does interfere). Make sure the bows are to the wind, and your rotation limiter is free. Clean the track on your mast, spray it with lube. Also, how tight are your battens? Overly tight battens can make the caps at the luff rub against the mast itself.

Hope this all helps...