We've told you in the past how to set up keyword bookmarks in both Firefox and Chrome. If you've only got a handful of keyword bookmarks, then the fastest option is to use single letters: f for Flickr, w for Wikipedia and so on. However, if you end up with dozens of options set up, you'll quickly end up needing to use two or three letters for most bookmarks.
The tempting option is to use obvious abbreviations -- lh for Lifehacker, am for Amazon -- and that certainly helps with keeping the shortcuts in your memory. However, setting up a pair of letters that are adjacent makes the shortcut faster to type. My most commonly used keyword bookmark is for Lifehacker searches, and I've defined this as zx. Not only are the letters adjacent to each other, they're near the Control key, which I will have just used to access the address bar.
There's definitely a balance to be struck here: for less frequent options, an obvious acronym makes more sense. But if you're searching a specific site multiple times a day (as I do with Lifehacker), choosing an adjacent pair (and using the Control-L keyboard shortcut to access the address bar) can save you a lot of time. (This point did get mentioned briefly in my original guide to setting up keyboard bookmarks, but it's worth reiterating.)