It's not easy. I've sent out many query letters for my first novel and had some close calls, but that's only in horseshoes I'm told. After reading some great materials on writing in general, I decided to take some advice and write for anthologies.
Actually, the only real money I made was from Spook Rock, my first novel and, The Lazarus Culture, my second. Most of the anthologies I've been published in were simply for the sake of making money for the publisher and getting my name known throughout the writing world. This is NOT a bad idea at all. If you enjoy writing in the horror genre as I do, it's a good idea to go to Ralan's Webstravaganza and and look for the word Anthology at the top of the page. You will be taken to the anthology page where you'll find the names of the anthology, the publisher, and what they're looking for from the author. Make sure you follow the guidelines.
If you're serious about writing, register an account with Permuted Press. There are some fine people there who have just about all the answers to questions you may have. You can actually talk about anything, not just writing.
There is nothing like seeing your name on a novel or on the index of an anthology. The good ones will put out a book that will make a writer proud be have their names somewhere in the pages. I can't tell you how many books I've sold at signings and simply by word of mouth.
A great book to help with your writing is Stephen King's "On Writing." It's simply direct and to the point with no foolish drivel that you get with other 'how to' or 'self help' type books. I have about $300.00 worth of research books as well, which include a good batch of Writer's Digest books like: Cause of Death, Body Trauma, Order in the Court, and Deadly Doses. I have these books because I believe that research is a very important part of writing. Know your audience. Your readers to be exact. Remember: Doctors, Lawyers, Nurses, Police Officers . . . all these people read. However, you're going to make mistakes no matter how much research you put into your work. The bottom line is that it's only a book. It's fiction. Do your best in the research, but don't be discouraged if someone nit-picks at certain faults they find. Reviewers can be very nasty when it comes to finding mistakes in your work. Just move on. Do what the wishguys do. Fi-git-a-bot-it!
A good 'young person's book' for a lot of fun in learning grammar is: The Transitive Vampire by Karen E. Gordon. She bills it as A Handbook of the Innocent, the Eager, and the Doomed. I received quite a few great comments by teens who enjoyed learning from its pages. If you have a young person who's interested in writing, have them give it a try. I don't think you'll be disappointed.