When reviewing, I try to keep a few things in my mind ...
First of all, I don't review all stories I read, only those I really like or those which have a potential to be great but for some reason the author 'forgot' about them. So it's like kicking someone in the rear to make them write further, so to speak. No, I don't leave the flames; if I don't like a story, I simply don't review.
Secondly, I always try to say something personal in my reviews; I think it's nicer for the author to read something that someone put a part of themselves in. A personal comment is just ... special for me.
I always try to say what I liked in the chapter, and ALWAYS make some predictions about the future chapters, that's just my quirk.
Hm ... I try to remember about greetings and thanks for the chapter, after all, someone who posted a good, interesting chapter deserves them.
I don't know if it makes any sense but that's my recipe for a review.