Before you write the review, naturally you first have to evaluate the product. Assuming that we're talking primarily about software reviews, at the moment, here's some of the steps you should take
Obviously, you need to install and use the software in whatever seems like the ordinary manner. At first, you can use it the way you would personally, but always keep the reader's concerns in mind. At first, follow the directions and create simple projects (the proverbial "hello world" application, flow chart, or other result), and gradually get more complex.
Read the documentation. I realize that this is anathema for a lot of technical users (particularly those who seem to be tapped for a review at work, because of their expertise), but when you're writing a review it is entirely necessary. You need to understand everything the product can do (or at least what it promises to do), not just use the features that appeal to you personally. (Remember that part about staying aware of what your reader cares about?) Plus, you can't put yourself in the position of reporting that an application lacks a feature, and have the vendor respond, "It's documented right there on page 42! "While you explore the features, look at what the product does - and also look at what the product doesn't do. It's easy to get lost in the feature chart of promises, and to become distracted from the necessary tasks that the product lacks.
For both yourself and your reader, note the difference between the features that are "need to have" versus those that are "neat to have." (Okay, so this lawnmower cuts the grass with a laser and has a connection to the Internet. Why would anybody need such a feature?) How well do these features address the problem to be solved?
