The J and K keys navigate through lists of items in Gmail, Google Reader, and even Google search results–without getting the mouse involved, which saves you point-and-click time. J goes to the next item down the list, and K the previous. J and K aren’t easy for your brain to remember, but they are for your fingers: most keyboards have a little nubbin on the J key, and if you’re a touch typist, your right hand’s forefinger rests on the J key. The J and K shortcuts move the cursor up and down in other (some old school) software too, like vim. Here’s how to give your J and K keys a workout in Gmail, Google Reader, and even Google search results.
In Gmail, make sure keyboard shortcuts are enabled for your account. (In Settings, on the General tab, check off the “Keyboard shortcuts on” radio button.) Then, when you’re in your inbox looking at a list of messages OR in an individual message, tapping J will move you to an older conversation and K to a newer convo. From there you can open, archive, and do more with your Gmail messages from the keyboard: Here’s the full list of Gmail keyboard shortcuts. Print it out and put it by your computer.
In Google Reader, J and K work by default. When you have a Reader item open, hit J to go to the next (older) item down the list, and K to move up.
Finally, if you enable the experimental keyboard-driven Google search experiment, you can also use J and K to move up and down through Google Search results. Once you’ve joined the keyboard experiment and run a search, there will be a little pointer on the top link in your results. Use J and K to move up and down the list. Once you’re on the link you want, hit Enter to open that link in tab or the undocumented Shift+O to open it in a new tab. See the rest of the keyboard shortcuts available in results in the screenshot above.