Things to avoid:

1) Words that have little or no meaning: When we write, we sometimes take on the same habits we have when we speak. Words or phrases that have little or no meaning fill space when we talk but have limited use in writing. Words such as kind of, actually, in particular, really, certain, various, virtually, individual, basically, generally, given, and practically give our brains a chance to collect our thoughts when speaking. When writing, we should have our thoughts already collected because this helps convey ideas more efficiently.

Example 1 Procrastination actually makes certain people really unsuccessful more than virtually any other particular habit. 

Edited Example 1 Procrastination makes people unsuccessful more than any other habit. 

Example 2 I am of the opinion that we should not prohibit children from talking in the hallways entirely and completely. 

Revised Example 2 We should allow children to talk in the hallways on occasion.

2) Redundancy: Often, writing assignments require a minimum number of words. Because of this, it is tempting to use several words of description instead of one wellchosen word with the same meaning. This redundancy, however, makes sentences awkward and interrupts the flow to a piece of writing. To write effectively, you must eliminate words that simply rephrase other words for no purpose. 

Example The football team made future plans to completely concentrate on the basic fundamentals of each individual position. Plans are always for the future; concentrating implies complete focus; fundamental means basic; and positions are individual. Therefore, the italicized words are unnecessary modifiers. 

Edited Example The football team made plans to concentrate on the fundamentals of each position. 

Some other common redundancies include whole entire, big fat, complete truth, terrible tragedy, pitch black, various different, true facts, free gift, and final outcome. Words also imply categories, so you can often eliminate a word that names a category. 

Example The dinosaurs that were green colored were few in number during that period in history. 

Edited Example There were few green dinosaurs during that period. 

3) Negatives: Changing negatives to affirmatives also eliminates extra words. Look for sentences that use not and see if you can rewrite the sentence to make it affirmative. 

Example NEGATIVE: She wore a sweater that was not different than mine. 

Edited Example She wore the same sweater as mine. 

Double negatives make your writing sound more confusing. Some words are negative by definition, such as the verbs preclude, exclude, fail, reject, avoid, deny, prohibit, and refuse and such prepositions as against or without. Using a combination of these negative words will make your point very difficult to understand. 

Example DOUBLE NEGATIVES: Without failing to refuse denying an invitation, you have not avoided precluding buying a gift. Edited Example By accepting an invitation, you have agreed to buy a gift.

Source: p.45-55 Smith, Brady. Proofreading, revising, and editing skills : success in 20 minutes a day / Brady Smith.—1st ed.