I'd like to talk about the negative side of submission: when it's not going well.
The truth of it is: the longer you are on submission, the lower your odds are of selling. Odds aren't absolute: longer doesn't mean no. It just means "less likely." There are only so many editors to submit to, and eventually you'll run out of fresh eyes.
If you don't hear something positive/have an offer in the first eight weeks on sub, your odds drop a bit. Not a ton, just a bit. Every month that passes, it feels like a book deal is further away.
My number one piece of advice, which is easier to give than to follow: work on a new book while you are on submission. It will keep you distracted, and should you not sell, you will have a new project ready for your agent when things are done. The more you look forward, the less you look back.
Now, I'll let you off the hook if you are not able to do this: I wasn't. While I was on submission with my third book (ie: my second time on submission), I didn't really draft anything new. Realistically I knew that if BRIGHTLY BURNING sold that my publisher might dictate my follow-up book (I was hoping for a two book deal, which is very en vogue right now). And it turned out I was right! But that's getting ahead of myself. I also didn't properly dive into drafting a new project, because once I hit about the three month mark of round one of submission, it became clear that I was likely going to have to revise before going on second round.
Revision between rounds is extremely common. The whole reason many agents strategically do small rounds of submission is to allow for revision if pass notes bring up common themes/issues.
The ability to revise between rounds offers good news and silver linings: namely, every time you start a new, fresh round of submission, your clock starts over! Now, it doesn't feel like that *to you*, because of course when you've been on submission from September to February and then start round two in March, as far as you are concerned, it is month six for you. But the editors in your new round seeing your book are coming to it completely fresh. It's new! And shiny!
I did not sell my book after five months on sub. But I did sell it only four weeks into second round of sub. It was a fast sale... it just took seven months, from start of sub to end.
My story is not uncommon--I have several friends who also revised between rounds and sold on second round of submission. There are authors who sell in third, fourth, or fifth rounds. Authors sell after six months, nine months, a year, a year and a half.
What happens if you don't sell your book on submission? You'll find that advice in the Worst Case Scenarios edition of #HowToAuthor