Make sure you have a good layer of kiln wash on the shelf. This is to facilitate the removal of glaze drips. Do not apply kiln wash to the sides of the kiln, or underside of the kiln shelves. The wash is likely to flake off and land on your glazed pieces.
A thick layer of glaze on the inside of a pot, and a thin or no layer on the outside will cause stress. The result is often a spiral crack up the sides.
If glaze pools on the inside of a pot, tension is created and the pot may crack or split across the base.
Pieces that are heavily glazed should be kept further apart during firing to avoid glaze running from one piece to another.