Enroll in composition classes at a nearby college, or enroll in an online course. You will benefit from having a professor of English correct your compositions. Read the notes he makes on your compositions to avoid making the same mistakes in the future. Take an advanced composition course when you have completed the beginning course.
Read insatiably. If you are interested in creative writing, read novels. If you want to be a poet, read the great poets and learn how poetry is composed. If you want to write discursive prose, read as much as you can in the disciplines that attract you. If you read a lot, eventually you will discover the genre that suits your writing style.
Write every day. Constant practice makes for perfect compositions. Start a blog, or keep a diary of your thoughts. Jot down ideas that come to you. Make a list of topics that you might like to explore with your writing. If you make it a practice to write every day at the same time, it will become a habit, and you will find it easier to write on the days you do not feel inspired.
Join a writers' group, and benefit from the interaction with others who enjoy writing. Let other writers read what you have written, and read their literary productions in return. By helping others improve their writing, you will also help yourself by learning from the mistakes others make and avoiding them in your writing.
Prepare your manuscript carefully, following the guidelines of each publisher, and submit it for editorial consideration. Consult "Writer's Market" for thousands of editors who are looking for material to publish. "Writer's Market" offers information about where you can publish a book, an article or even verses for greeting cards. It also lists literary agents.
Consider self-publishing. Some of the world's most famous authors self-published their work, including Stephen King, Edgar Allen Poe, Benjamin Franklin and Mark Twain. Many companies will publish your work for a reasonable amount of money, particularly if you follow a print-on-demand model that charges for specific quantities of books rather than larger lots.