Be concise. Repeat a word or phrase only when it is needed for emphasis, clarity, or coherence.
Conciseness---using words economically---is fundamental to clear writing.
WORDY In the early part of the month of August, a hurricane was moving threateningly toward Houston.
CONCISE In early August, a hurricane threatened Houston.
Needless repetition of words or phrases distracts the reader and blurs meaning.
REPETITIOUS This interesting instructor makes an uninteresting subject interesting.
CONCISE This instructor makes a dull subject interesting.
REPETITIOUS I am a 17-year-old high schooler who is a junior at West High, and I play soccer on the high school soccer team.
CONCISE I am a 17-year-old junior at West High, where I play on the soccer team. (If you were tight for space, you could probably cut "17-year-old," since 80 percent of juniors are 17, and the rest are within a year of that age.)
When you are really looking closely at letters or articles for newspapers or magazines, you can usually find redundancies even after several rounds of editing. This is especially handy when you need to cut pieces or letters to fit onto a page. For example, you might find a sentence like, "We visited a farm out in the country." Or, "We went to a NASCAR race at a racetrack." Where else would these things be found?
I've noticed some common redundancies like, "You can e-mail me at my e-mail address, email@example.com." This is plainly an e-mail address, so it is just as informative to say, "You can e-mail me at firstname.lastname@example.org." Or you could even say, "You can contact me at email@example.com." It's not a telephone number or a post office address. Given this information, how else could someone contact you but by e-mail?
Rules 21a(1-3), 21b and 21c offer lots of handy tips for avoiding wordiness, redundancy, tautology (the use of different words to say the same thing).