"The greatest part of a writer's time is spent in reading, in order to write; a man will turn over half a library to make one book."--Samuel Johnson
You must read--what others are writing, especially of your peers, what the market is publishing, and what the library will have to offer you, which is enough for several lifetimes. Don't be overwhelmed by all this, but don't ignore it either.
Much of the process of marketing a book has been taken out of anecdote and personal contact and made into a business. There are in fact a variety of fine resource books available today that will help you as a writer determine your public course of action.
And don't forget the Internet. In two years, this may be the first resource to check. Right now, it is always surprising, with plenty of information to offer. The validity of Internet information can sometimes be suspect, but as a resource it has everything to offer. Explore with some caution--but explore!
DVICE. No matter how you or why you may think these somehow do not apply to you, think twice--or just think. Any information you get is information you did not have, and it will be useful, whether directly or intrinsically. It will be imperative, as you go seriously into the profession, that you look through these books and online sources and spend some time with them. They have good, informed advice about the profession. They aren't simply collections of addresses. Some books to consider, depending on your genre and interest, would be:
A book such as Writer's Market, for example, will give you all kinds of specific information, from sample query letters to how much to charge per hour for writing work that you might do. There will be information on copyright, tax issues, and so on. The point it, look at these books--really look at them--and think about purchasing the one you like best so you can refer to it at home. Some of their current information may go out of date, but their general advice is long-term.