Dishwasher doesn't remove all the soap
General suggestions:


use powdered soaps (not liquid)
make sure you are using a rinse aid (jet-dry)
make sure you aren't using 'too much' soap
run the dishes through a cycle with vinegar added to the dishwasher
look on the dish soap aisle for some powered 'soap scum' removal powders that you can adde to the dish soap. It's often a citric-based product in powder form