Clearly defined purpose and goals of the research study at the beginning of the document. Headings used to separate different sections of the document. Lower case for the text, upper case for emphasis. Words are short and simple. If there are long or complicated words, replace or define them with more commonplace synonyms.
Sentences are short, simple and vary in structure.
Shorter words in longer sentences can also be confusing. Try to proofread for overall understandability. As a basic guideline, if a sentence has more than 20 words, it is too long. Whenever possible, write in a conversational style, as if you are talking to the potential research subject. Remember, if the potential subject has to read a sentence more than once or twice, it needs to be revised.