This is a very simple thing but it can be useful for folks who are still using mostly arrow keys. It finally clicked for me when I started using Tridactyl for Firefox :)

Most of the time you need down and up motions so you rest your index finger on J and middle finger on K. J looks little bit like a down arrow (mnemonics jown and kup don’t seem very intuitive to me). So now you have the main arrow keys assigned to your fingers. Naturally you rest your ring finger on the L key and when you occasionally need to move left just move your index finger to the H key.