It might sound strange, but reading newspaper and magazine articles is often better practise for your writing than reading novels. Although novels help to instill creativity, the opinion columns of good newspapers expose you to a very varied range of styles. Newspaper columnists and journalists are often constrained for space, and their articles must always be very concise and effective -- a highly desirable skill.
When sitting for exams or writing essays, many of the titles presented deal with current affairs. Newspapers will expose the world's affairs to you, and you will be confident with newly acquired knowledge when tackling these essays.
One of the most important aspects of writing is the use of anecdotes. When you've got knowledge, flaunt it. Do this by mentioning an opinion of a columnist you have read, for example, as a little sidenote in an essay. This keeps your writing interesting -- and your reader glued to the page.
The
New York Times website is good source of free and very well-written articles.
Here are some others:
Nico Colchester (Fellowship for Young Journalists)
Telegraph Opinion
Observer International