Science fiction author Robert A. Heinlein, long ago, came up with five simple rules for writing. If you just Google this, you'll come up with plenty of websites where these are listed. The following I found on one of Dean Wesley Smith's blog posts:
1) You must write.
2) You must finish what you start
3) You must refrain from rewriting, except to editorial order
4) You must put it out on the market
5) You must keep it on the market until it's sold
Let's expand on these a little, as I add my thoughts to the mix for clarification, even though the rules are simple.
1) (self-explanatory - if you wanted to be a pro football player, you'd better be throwing around the old pigskin. Writing is no different)
2) I don't know how many people I meet tell me they've always wanted to write a book or have started. Have they finished? No. Finish the damn book.
3) There should be no rewriting in the first draft while you're writing. You WILL need to edit once the book is done.
4) You've spent all this time writing your story. Spend a little time and find out where it should go--unless you're going to self-publish. Then, if you do that, research ways to do it right. Check out Joanna Penn's blog "The Creative Penn" for info on how to do this right.
5) If one place rejects you (assuming no self-pub right now unless that's the direction you now want to go) send it right back out.
Happy writing! Keep writing! Then, once it's edited, let it fly!