If you care about books, you should know the story of Johannes Gutenberg.

Can you remember how to spell these? Grammar Girl has the trick.

A memory trick to remember the spellings, plus rules for when "personnel" is singular and when it is plural.

Grammar Girl has a Quick and Dirty Tip to remember the difference between "tenet" and "tenant'.

Grammar Girl has memory tricks for remembering the differences.

"Disinterested" and "uninterested" have different meanings, but people are starting to confuse them. Grammar Girl has a trick for getting them right. 

Although the "in-" prefix can be negative, it's not in this case. Grammar Girl explains this and other linguistic phenomena.