It's pretty easy to remember 20 random words, you just have to relate them to eachother and see it your mind for just a fraction of a second, then when you think of 1 word you think of the next and the next, for instance:
You have the words: banana, car, newspaper, sausage, pen, tree, watch, tie, television, football
Now imagine a gigantic banana is driving a car along the motorway. Be careful not to picture the words banana and car. You need to see the action you've selected - the huge banana driving the car.
The next item on your list is newspaper. Assuming that you already remember car, you now need to form a ridiculous association in your mind between car and newspaper. For example, you are driving a huge rolled up newspaper instead of a car. Now picture this in your mind.
Sausage is the next item to remember, so you now need to form a ludicrous association between newspaper and sausage. You could picture yourself reading a gigantic sausage which has lots of news printed on it.
Next on the list is pen. Associate it to sausage. See yourself trying to write with a sausage instead of a pen.
The next item is tree. Picture millions of pens growing on a tree instead of leaves.
Watch is the next item on the list. Picture yourself looking at your watch and see that there is a tree growing out of it, with roots curling up your arm.
Tie comes next. See yourself wearing an elongated wristwatch instead of a tie.
The next item to be remembered is television. Picture yourself with a television hanging around your neck instead of a tie.
The final item on the list is football. See a football match where the players are kicking around a television instead of a football.
If you have really tried to see all those pictures, you will now remember the list of ten items in sequence, both forwards and backwards.
Just try it, try thinking of the huge banana, immediately you'll think of the car, then you'll think of yourself riding a newspaper instead of a car, and so on, same applies for doing it backwards, think of a football and immediately you'll think of the television you're watching football on.
This is deeply explained on this site which I just read thoroughly:
http://www.vlaardingen.net/~tom/Mainmenu.htm