Studies have shown that people can remember between five and nine items at a time depending on the information. By using a range of adding two or subtracting two, we get the number seven.
In general, people can only remember seven things at one time. When writing instructions and steps, we should keep the number seven in mind. Try to keep instructions to seven steps or less. If a set of instructions is long, try breaking it down into groups instead of one long list of steps.
It is also good to keep sentences 21 words or less. If a sentence looks complex, it probably is. Do not force the reader to read a sentence more than once to understand its meaning. Studies show that people retain information from sentences no more than 21 words. Can anyone guess what 21 is divisible by?
Here are links to more information about the studies and memory:
http://www.nwlink.com/~donclark/hrd/learning/memory.html
http://www.sheridanc.on.ca/~sherman/rap.dir/weeks1to4/Cutfog.html