Avoid cliches like the plague. Employ the vernacular. Contractions aren't necessary and shouldn't be used. One should never ever generalize. Tell me what you know.
Comparisons are as bad as cliches.
Do not repeat yourself in any case. Be more or less specific whenever possible. Understatement is always the absolute best way to put forth earthshaking ideas. Analogies in writing are like feathers on a snake. The passive voice is to be avoided.