h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

As mentioned in the article, two letter words are important. In fact, they are the most important thing to learn if you want to improve your score (there are around 100 of them). There are two reasons for this.

HIGH SCORING LETTERS

The first use is to get rid of nasty letters in good places. The most useful words for this are QI ZO JO AX EX OX XI XU. I have often scored 50 points by putting my X on a triple letter score and making a word in each direction. The only letter in the alphabet which is in no two-letter words is V, making it by far the worst letter in the game.

A word of caution: these words are all from the Chambers Dictionary and the Official Scrabble Words. If you play with a different dictionary, some of these may not be allowed (PH springs to mind) so make sure you know what is in your dictionary.

PARALLEL PLAY

The second use for two letter words is in parallel play. This refers to the technique of placing your word alongside one already on the board rather than through it. When both players know all the two-letter words, almost all moves tend to be made in this way since it gains you a lot more points.

The downside of this is that games tend to progress along the main diagonals and it can be very difficult to find a place to go near the end of the game. I have had more than one game end prematurely when neither of us could find a single place to move.

is that once you know what two letter words are allowed, you can place your words parallel to other people's, giving you many more options for places to go and getting some extra points for the words made in the process. Words like AA AE EA etc are useful here.
When both players know these words, almost all moves tend to be parallel