Lightroom has a large number of 'one key' features that make it powerful in all its modules such as using the TAB key to cycle through or hide the side panels in the various modules.

Modifying some these 'one key' commands with a the usual Shift, Alt, or Ctrl combos adds to very quick changes in the function of the Lightroom.

There are some slight differences in these from Module to Module and instead of memorizing them all or creating cheat sheets or using (shudder) keyboard overlays, there's one keyboard command to memorize above all else:

' Ctrl / '

This will pop up a 'cheat sheet' in a context/Module sensitive form to remind you what the quick way to cycle between views or panels is for the part of the Lightroom you are currently using.

Another very useful key and this is a single key command is using the ' ~ ' to toggle the Flag status of a photo.

Happy editing and sorting!