Make it both memorable and secure:

One way … is to combine the ideas of a password and a passphrase into a so-called mnemonic password. This is a string of apparent gibberish which is not actually too hard to remember. It can be formed, for example, by using the first letter of each word in a phrase, varying upper and lower case, and substituting some symbols for others—“8” for “B”, for instance. (“itaMc0Ttit8” is thus a mnemonic contraction of the text in these brackets.)