Breaking in a baseball glove gives the glove a customized fit while making the leather soft and flexible. Many glove conditioners are available, but Vaseline--a petroleum jelly based product used to clean and lubricate--makes a great glove conditioner as it softens and protects the leather. The break-in period is crucial for preserving the glove and allowing it to last for years to come. Several glove and leather conditioners are available, but Vaseline is a great choice.
Apply Vaseline to every part of the glove using a cloth or rag. Leather acts like human skin, and the Vaseline can help protect the leather from weather, dirt and moisture. Work the Vaseline into every part of the glove and wipe off excess with the rag. Allow the Vaseline to work into the leather for one to two days.
Play catch or beat the pocket with a rubber or wooden mallet every day or as much as possible. Apply more Vaseline to the pocket after playing catch. This will help to make the leather flexible and form to the ball in the pocket.
Store the glove with a baseball in the pocket and wrap a rubber band around the glove to keep it closed. This allows the leather to form around the ball and helps to speed up the break-in process. When you are not playing catch, keep the glove stored like this for at least two weeks. Some gloves may take longer to break in based on the quality of the leather.