Read critically and learn from the best by reading from the best. Learn to do this on your own without a formal class. Write down thoughts as you read. You can't be a good writer without being a good reader. Continue to read as you teach yourself how to write.
When you start writing don't wait for inspiration. Write every day for at least two hours. Don't make it into something lofty. Think of it as a regular job. If your writing is lousy at first don't get discouraged. You need to write 100,000 words or so before it's likely you'll find a voice and develop enough craft that you'll write something others will find worth reading.