Glove care can be broken into two major areas: in-season care and out-of-season care. During the season, a ball should be kept in the pocket of the glove whenever it is not being used. Because the ball can fall out of the glove if the glove is just thrown into an equipment bag, I recommend putting the glove with ball in a side compartment in which they will fit. If there are no side compartments in the equipment bag, then wrap the glove and ball with a large rubber band. If the glove is put away too often without a ball in the pocket, the pocket will disappear or deform and the glove will not catch the ball as well as it should. If that happens, then you basically have to break the glove in from scratch (see the Related Article below to review how to break in a glove).
Prior to using the glove before a practice or a game, check the laces and the webbing to make sure nothing is working loose. If a knot is untying, then take a couple of seconds to retie it. This “as used” maintenance is crucial, otherwise laces can work completely loose and have to be re-threaded through the glove which is a major pain and can be quite time consuming.
After the season is over, it is best to re-condition the glove, as there is a good chance that the leather will have dried out some during the season, particularly if the season has been during a hot, dry summer. Rub mineral oil or other leather/glove conditioner liberally over the outside and inside of the glove, then put a ball in the pocket, wrap the glove with a rubber band, and place the glove somewhere clean and dry. About a week before the first practice of the next season, rub some more conditioner on the glove.
On a final note, never leave your glove out in the rain! Water and leather generally do not mix. However, if a glove does get soaked, let it dry out most of the way and then apply a lot of glove conditioner to it.