Organization - Make sure your ideas flow in a logical order. Use connecting words so that the ideas flow from one sentence to the next and one paragraph to the next. Make it easy for your reader to understand and follow what you are trying to say.
EDIT!! - Always allow time for editing. Sloppy writing communicates sloppy science, so put your work in the best light by fixing mistakes before you share it. Leave a break between your first draft and coming back to edit your work. Edit at least twice - once for grammar and once for structure. Look for different things each time you edit (spelling, punctuation, unnecessary words, incomplete sentences, ideas out of logical order, etc.).
Length - You may want to write a first draft without worrying about the length, and then shorten it by editing out extra details that aren't important.
Impact - Never start a sentence with "It is" or "There are." Other alternatives can always be found. Use real verbs and nouns – they give your writing greater impact.