Moving on from all the general stuff, we get to some specifics. Now, since I write "Comprehensive Reviews," I can't provide any specific advice for any other form. I assume that the emailer likes the way I review books, so I'll offer some insight on that front.
When writing a review, I immediately place into focus three things:
The basic story, the plot, etc.
What's good and what's bad.
- Like/Not Like
Did I like it or did I dislike it? Why?
On top of these elements, however, I tend to toss in some personal reaction. I like to tell the reader my personal reactions to elements within the story. Was a particular scene emotionally gripping? Did I cry? Did I grimace? Did I actually have a visceral reaction to something that a character did? I consider this to be an important aspect of my reviews because I get the sense that readers want books that are engaging on multiple levels. If a book did something for me on an emotional or physical level, that's something they'd like to know so they don't go and buy some book that turns out to be emotionally empty. Personal opinion doesn't have to be specifically in this vein, though. You can fiddle with the imaginary "conventions" of book reviewing all you want.
What you do in your reviews, however, is up to you. Don't let me determine how you write your reviews (or anyone else, for that matter). Sit down and give it a shot. When I started writing reviews, I was horrible (I've gone back to look). I don't consider myself a particularly good reviewer today, but I can see how I have improved. There's nothing wrong with starting and sucking (just like in writing fiction).
What is important is determining what you want to do with your reviews, how you want to present them, and then doing it. Everything else can fall into place one piece at a time.