The best way you can become a better writer is to kidnap a famous write and force him/she write for you. The or 20 years of training...
The most effective way to write better is to read and speak better. If you are writing in English then it is a must that you are comfortable with the language. you should know everything from grammar, punctuations, etc. Brush up on your writing skills by watching the news or reading books, this way you will get a general feel of how things should be properly written.
Practice as they say makes perfect, but you could always look at the style of other writers and get ideas from that
To become a better writer, you must learn every aspects of every topic you ought to know. Make yourself open for new topics so whatever topic that will be given to you, you can learn just anything.