A review or test is a text, video or all together that tells you about nuances of a certain product with the help of "live" photos and personal impressions. And personal impressions are the most valuable thing in the review — those trifles that cannot be found in the official description.
If you've never written a review it's better to find examples Если вы никогда не писали обзоры, найдите примеры хороших обзоров on Habr or other websites.
You should actually use the device, service or software you are talking about. It always feels like there's no depth when the review is written "by photos". While you're using it, write down what you like and what you don't, otherwise you'll definitely forget something interesting.
Try to find everything on the Web that is on your product: development history, twists and turns of the manufacturer, rumors and facts. You may not use any of this in your review, but additional information will definitely give you the broad picture.
Write easily, without nerdiness. Choose clear wording, make simple sentences. Where you can easily desribe thing without terms, use simple English.
If you feel you can not write expertly about some aspect of a device or a program, take a comment from a specialist. This will even add value to your content.
Remember reader's interests. Write about what is really important, first of all — nuances you cannot learn about without using the product for a long time.
You shouldn't write about the packaging of your device — usually nobody cares about the box and throw it away at all. Also don't write about obvious things: why say the "Continue" button is in the bottom right corner of the window if everyone can see it on the screenshot.
Mindful guys who appreciate readers' time and want to make a good impression, work according to this scheme:
Draft → leave to rest → read once again → rewrite → repeat several times
Pick the latest gadgets, services, cars, computers, drones, robots and so on. It makes no sense to write about what everyone has been using for a year. The value of the review is that it gives people something about the product before they buy it. Or if the subject of the review is especially expensive, rarity, and not for the average consumer at all, it gives readers a general idea of an unusual product and entertains.
The only limitation is a completeness of the review. Ask yourself honestly: have all important questions been answered? If not — keep writing and reveal the details.
Read the text and ask yourself: have you written anything unnecessary, trivial and obvious? If so — cut the unimportant.
It's not so important how many characters you will finaly get, but on average it turns out 6–10 thousand.
Ideally the illustration is a piece of content you can't get rid of and not to lost part of the meaning of the whole review at the same time. An illustration is not just for beauty, but for the reader to easily imagine what you are talking about. Assume that the photo should answer not only the question "what" but also "how".
The better the quality of the photo and the less noise it makes, the better. The "clearer" the background, the clearer it is.