I made a One Page list of Scrabble Usefulness [pdf] listing the most important scrabble words in a very compact form. This list is based on one given out by the National Scrabble Association. I've reformatted it and added some interesting new information.
The two letter words are in bold, and the letters to each side show front and back hooks: AA is a word (a type of lava), and so are BAA (noise a sheep makes) and AAH (exclamation), AAL (shrub), and AAS (plural of AA). If you're starting out in scrabble, don't worry about the hooks yet -- just memorize the 96 2-letter words. The second best thing to memorize (but much less important) are the "U-less Q Words." Dumps are useful later: "I Dumps" and "U Dumps" list all the 3- or 4-letter words with several i's or u's; "Vowel Dumps" lists all 3-, 4- or 5-letter words with more than 3/4 vowels.
If you just want the two letter words, here they are:
aa ab ad ae ag ah ai al am an ar as at aw ax ay ba be bi bo by de do ed ef eh el em en er es et ex fa go ha he hi hm ho id if in is it jo ka la li lo ma me mi mm mo mu my na ne no nu od oe of oh om on op or os ow ox oy pa pe pi re sh si so ta ti to uh um un up us ut we wo xi xu ya ye yo
To move from parlor play to competitive play, you should learn, in order:
Two Letter Words with Definitions