Make sure the origin of each object is in a sensible place. Origin to Center of Mass also often works well for this. Also make sure the objects’ scales and rotations are applied before simulations are done (ctrl-A in object mode) and that you’ve gotten rid of any duplicate vertices in the meshes (in Edit mode select all, W>Remove Doubles). Those three steps tend to solve 90% of simulation problems. And rigging problems, for that matter.