Read, Read and Read
For any writing it is must you know a lot, and by reading more books, your reading will improve and so will your ability to sum up the entire book into a summary or a few paragraphs. This is the beginning of writing reviews.
Read Reviews To Pick Styles
Alongside reading books you should also read book reviews by senior writers. This will help you to pick style and it is possible that you might read some reviews of those books, which you have read and get to know how the information in the book was concentrated in a few paragraphs.
Write Reviews for Practice
While you read senior book review writers to pick the style, you can write a few reviews for the sake of practice, and if you know a writer who is willing to check your work, you can share your pieces to get them critically viewed. This will hone your skills and writing style.
How to Approach Your Work
While you read book reviews of senior writers, you will see a majority of them start with giving factual information, and then writing other ingredients. They pick the most interesting part of information, summarize lengthy chunks and make the writing an easy read and understandable. The writing style is not what has been adopted in the book, but more simplistic and journalistic type that readers find easy and interesting to read.
When you think you are ready to get your work published somewhere, look for freelance opportunities. It is great to start, as it will help you get your work published after some editing and this will help you learn. It is possible you might receive comments from readers or critics and it hones your writing style further. Nevertheless, it will boost your confidence and a belief in your writing, a must for any writer to write better.
Write As Full-Time Writer
After doing some freelance work, you can start writing regularly with any periodical or newspaper, or even in some journal. It is better to start with a newspaper but if it is some academic work, try to write for journals as well.