Instructions
With a Group of People
Have everyone sit in an orderly fashion. Circles work best because it is easy to figure out whose turn it is.
Appoint a leader. The leader must choose a starting word, or you can prepare a set of index cards with random words. The leader says the starting word out loud. If you have a set of cards, the leader picks the first card and reads the word printed on it.
Play passes to the person next to the leader, either to the left or right. This person says the first word that pops into his head. The next person responds to this new word. Continue around the circle. If there is a pause, for laughter or confusion, choose a new leader to restart the game.
Add restrictions to make the game more interesting. For example, you can make a rule that all words have to be a particular part of speech. Or, you can decide that all words must begin or end with a particular letter.
Online
Search for an online free-association game.
Type the first word that comes to mind when presented with the cue word, but pay attention the words that are off limits. You cannot type these words.
Come up with more word ideas until you and your randomly assigned partner come up with the same word.