Here is a link to the Colorado State University writing
website. It gives you easy to understand guidelines for science writing.
Here is a link to The Journal of Young Investigators' website that gives more details. Its a PDF file. Nevertheless, basically, anytime you are writing a scientific paper, you want to use the format given here.
Your audience will most likely be people who are already in the profession and these people are used to reading medical literature all the times. Because they are already adjusted to a certain format, you not not want to try to reinvent the wheel.
For example, once they see the article, they may look at the Title. If the Title is of their interest, they may continue to read the Abstract. Once they read the abstract they will go directly to the conclusion - to view what the results are. They may not go into detail until later. So, whatever you do identify your audience, first. The remainder of the paper will fall in place.
In scientific papers, you do not have to worry about explaining anything but procedures. Definitions only if they are unfamiliar to you audience. You do not want to write the word DNA and write "where all cell's information is kept" to reader who all have PhD's. To them it will be offensive. So, just concentrate on giving you summary, the method of how you come to this conclusion, and the results.