According to Stephen King and many other writers, you need to read as much as you can. If you don't like to read then you're not going to become an author. It's essential. Yes, reading helps with grammar, spelling, punctuation, and vocabulary. It also helps with learning literary and genre elements, how to develop characters and plots, and other essential things you'll need to know when writing a novel. It's there before your eyes, in novel form, and most likely done successfully. You learn the different writing styles that authors use. You can study how they caught the reader's attention. You learn how they keep suspense in a page-turning novel. You also learn what has been done a million times over in that genre and try not to repeat it because it'll make your novel unoriginal. It also gives you the chance to differentiate your novel from everything else on the shelf, so that you have a better chance of being published.
You've probably been out of school for a while, so go to the library or bookstore and pick up grammar book, thesaurus, and dictionary. I haven't had an English class in years, since I was a freshman in college, so I have a grammar book by my side. Stephen King says in his book On Writing that the only writing book that's good enough for him to recommend is Strunk and White's Elements of Style. You can buy the updated version at the bookstore and you can view the public domain version here: http://www.bartleby.com/141/
My advice is to keep writing. That's how you get better. The thing that sets you apart from others on Answers is that you know when your writing stink, so that leaves way for you to improve. There are many teens who post their work here to think it's the best thing every written, all the while ignoring all the grammar issues and misspellings. They're disillusioned and it'll take them a while to get better since they don't see anything to improve in their writing. You, on the other hand, can greatly improve because you recognize that your writing isn't perfect and can be better. That's a good thing. This is what most writers have to endure during their first forays into writing. It's common and your case isn't special. Buy some how-to books, join so writing forums, and start researching how to write a novel. The more you write then the more you'll improve. After you've finished editing one novel then start another one and keep writing. Most published authors start out writing crap before they begin writing publishable material. It's part of the learning process, and you need to go through those stages before you can master the skill.
You're new to reading, so continue reading and read as much as you can. I didn't start reading regularly until the last two years of high school. Over the years, I cut down on how much I read, but I've picked it back up. Read a few classics. I recommend Pride and Prejudice by Jane Austin, if you like romance. She has some complex characters and you can analyze how she made them so complex and use that to help develop your character. Analyze the books you read and study how the authors handled different elements within it. A good exercise to get you started: read some books and then copy the first two chapters of them. This will help with writing style and help you learn some of the elements so that you can duplicate them with your own novel. Once you get the hang of it then you'll be able to develop your own style of writing and implement those elements effectively. Keep in mind that when giving work to family and friends that it's subjective. If someone doesn't like to read romance and you wrote romance, then they might not like it. So give it to people who like reading the genre you write. Good luck.
No, hooranim is WRONG about publishers not caring about grammar. I take that he hasn't done his publishing research? I've seen literary agents say they've rejected people because their work is full of bad grammar and/or misspellings. Don't embarrass yourself like that by sending off work with basic errors. Yes, agents have even told stories of how they've turned down great storylines because of bad writing. Bad grammar is a sign of weak writing, is what I've learned. Also, publishers aren't going to go around correcting your work like your high school English teacher would. Your work needs to be 95% publishable before a publisher will even buy it. If you need too many edits and corrections then they'll reject it, no matter how great your plot/concept is. You'll get all kinds of bad and erroneous info from Answers, and most of it comes from teens who can't write to save their lives, and who are just guessing or making assumption about the industry. I've actually done my homework - months of research - because I'm serious about trying to get published. You also need to do your research so you can discriminate between the good and bad info.