Following are few suggestions for you:

1- Start building your vocabulary.
Take any word list and learn 10 words daily . Vocabulary.com is also a wonderful site for enhancing vocabulary.It helps you in building word list by pasting the material you want to learn.

2- Read
Read,Read,Read.You can read about anything that you find interesting.It doesnt matter if you feel that the material is not directly related to the CSS Syllabus.

Reading is a must for good writing.You know children keep on Listening for couple of months before they start speaking themselves.Similarly,You need to read the work produced by good writers to build up a good written expression.

3- As far as Dawn is concerned. It is indeed bible for CSS as it will help you in preparation of all subjects.Being a beginner, there are chances that you will find reading newspaper a boring task. Therefore, take things slow.Start with headlines and one editorial/opinion article per day.Underline the difficult words and learn their meaning.

Once you develop a sense of comfort with Newspaper reading.Start reading international page (It will help you in solving MCQs),Business page and as much opinions/editorials you can read.

Don`t forget to save important news articles for further reference. If you are reading newspaper in hard copy.Cut the clippings of articles and arrange them topic wise in a file. Contrarily,If you read newspapers in soft copy, Use Evernote application for arranging and saving articles.

4-Have Patience. Good written expression is a skill and like all other skills e.g driving and cooking, it takes time to develop. Therefore, Never expect quick results and instead of being disappointed with slow progress,Just keep on working.Best of Luck!