General guidelines

To determine how long or how detailed a text block should be, consult previous publications from your target journal, preferably focusing on articles with a similar design and/or topic
If you state a fact, the sentence necessarily has to be backed up by a reference
Before you start writing the Introduction and Discussion sections, perform a thorough Literature Search by first going through the recommended PubMed tutorials
Use short sentences with a simple structure (subject - verb - object). Rule of thumb is that if a sentence is bigger than two lines, it is too big. Use active verbs
Rather than writing about specific studies, make broad statements and back them up by a series of citations
While citing reference in the text, preferably cite it as author and year (Harvard style of referencing). The style of citing and writing references can be changed later as per the journal requirements
It is good practice to be as descriptive as possible in writing Methods section while drafting the manuscripts during initial stages