[h=2]Breaking in a new wetsuit[/h]
Seems to me the question is not one of "breaking in" the wetsuit, but rather one of proper maintenance to help keep it "new" as long as possible.
Rinse thoroughly in clean water after every dive session. Make sure the zipper(s) are free of any crud/sand/accumulated salt. Apply a small amount of dry lubricant ("dry" silicone or parafin zipper wax) on the zippers. Some folks (like me) believe that an occasional spraying of an aqueous silicone product will help prolong the neoprene life. Dry your suit inside and out completely before storage. As much as possible, store all wetsuits in a cool, dry place with good ventilation, out of the sunlight. If hanging your wetsuit in storage, use the manufacturer provided (or a better grade if possible) suit hangers with broad shoulder bars. (Lots of folks are opposed to hanging wetsuits long term because of stretching. They prefer to let the suit lay completely flat -- on floor under one's bed, for example. In any event, don't fold or crease your wetsuit for long term storage.)