Establish guidelines first. Write your book, edit it until it's flawless in spelling and grammar errors. When you're through editing by yourself, find a disinterested person having expertise in the field to edit it for you. Many writing forums are available on-line to do this and it won't cost you, but many of those writers are beginning as you are.
When your book is ready and as perfect as it gets, obtain a Writer's Market book either at your library or book store. Select the best literary agent you can find that has specific needs for the genre and type novel you've written.
Follow all the submission guidelines found in the Writer's Market and check the agent's web page for their specific rules to submit your manuscript. Some agencies only accept manuscripts at certain times of the year; others have closed.
Then write the best query letter you can. It should surpass the opening paragraph of your novel so it will attract and keep the agent's attention to read further. Remember, if your query letter is amateurish and filled with incorrectly spelled words, the agent probably won't get beyond the first sentence.
To help you with query letters and manuscript submissions, consider buying "Formatting & Submitting Your Manuscript" by Cynthia Laufenberg. You won't regret such a purchase.
Good luck.