Dishwasher not draining: GE, Whirlpool, Bosch fixes

Clean the filter: most modern dishwashers have a twist-out cylinder filter under the bottom rack. It's the #1 cause.
New garbage disposal? The knockout plug in the disposal's dishwasher inlet must be removed. Forgetting it is a very common cause right after a disposal install.
Run the disposal and clear the sink drain. The dishwasher drains through it.
Drain hose: check for kinks and make sure there's a high loop or air gap so dirty water doesn't siphon back.
Bosch: a blinking E24/E25 means a drain blockage. Check the filter and the pump cover under it (a spoon-handle tab).
Hear a hum but no draining? The drain pump is jammed (glass shard, seed) or failed. That's a standard, worthwhile repair.