Use active voice, rather than passive, whenever possible. The active voice allows your reader to understand that the subject is performing the action, whereas the passive voice shows that the subject is receiving the action. Although the passive voice is not grammatically incorrect, it slows down the writing and isn't as clear as active. There are few cases when passive voice is necessary.
Avoid tense shifts. If you're writing in past tense, stick with it unless there is some clear and obvious reason to switch to a different tense. In that case, be sure the reader knows why you are switching.
Create cohesion between your paragraphs by using solid transitions. Using words such as therefore and however allow you to link the end sentence in one paragraph to the beginning sentence in the following paragraph. The key is to have each idea build off of the previous idea you have written. This way, your writing is clear and your ideas flow consistently through the paper.
Place punctuation in sentences where needed. Common errors include using too many commas, or not enough. A comma is commonly used to connect a dependent clause to an independent clause, or to separate items in a list, among other uses. Other common punctuation marks to consider are colons, semicolons and dashes. Be sure to end your sentences with proper punctuation as well. Statements and abbreviations require periods. Questions require question marks. Exclamation and imperative sentences require exclamation marks. Always use correct capitalization as well.
Incorporate correct style into your writing. Style includes sentence word order, parallelism and sentence-length variation. Be sure to use conjunctions, such as "and" and "but." Also, be consistent with the tense you are writing in, as well as noun/verb agreement, and noun/pronoun agreement.