Come, sit around the campfire. I will tell you something I learned from a million years ago when I used to work in acquisitions (meaning, I read slush and sent rejection letters and hurt preshus feelsies).
Submissions is like dating.
Really, guys, stay with me here.
Submitting a book to a publisher is like asking someone to the prom. Your success is dependent on a number of factors, only a few of which you have real control over.
Would you walk into a room and ask out every person in there in the hopes of getting one to say yes? Um, you could, but that's not very effective. Everyone would see what you're doing.
So now you're staring at this room of really pretty people. Okay, they're not all pretty. Some are ugly, but they'll be your back up choice. Do you just randomly ask them all out? Or do you wait and listen? Most are looking for a very particular kind of date, and if you spend some time around them, you'll learn what they want.
If you browse any publisher's catalogue, you'll learn what they're interested in. If you pay attention and follow agents on Twitter, you'll figure out pretty quickly what it is they like in a book, and what I don't. There's no big mystery. They often blog in detail about what makes them take certain books.
Now you've settled on a few possibilities for this prom date. You're both into the same things. You're exactly what they're looking for in a date, and they're totally hot. Now is when you run over and beg them to date you! Apologize for the fact that you live in a basement and have never dated before in your life, and don't bother combing your hair or anything.
Um, or you could clean yourself up and approach them respectfully.
First impressions count. You need simple cover letter, not long and rambly, that contains all the information they need to know about your submission. You don't need your life story in there. This isn't a discussion of marriage--this is a DATE, so to speak.
If someone you ask out says no...well, just tell her she's an idiot! You don't need her anyway! Like you even wanted to date her in the first place--ha! You'll just go...date yourself. That's the NEW way dating works--people just date themselves. Plus, she's kinda funny looking. You should tell her that too, and point out that other guy over there who's way hotter and just tell her that he's already accepted you anyway.
Or you could beg and plead. That'll work. Ask your friends to call her at all hours of the night and tell her what a GREAT prom date you'll make! Maybe if she just knew you better.
And you could ask her a bunch of times why she won't date you. Is it your hair? Your clothes? Is she not into your gender? Is it your breath? Oh, she must tell you why! And if she doesn't, maybe she just doesn't mean it. Maybe you should just tell her that you're going to the prom together no matter what.
Um...alternatively, you can thank her for your time and move on.
Listen, kids: no means no, and yes means yes. I've dealt with all of the above. None of it is attractive to a potential publisher, save the last point.
It sucks major hairy goat ass to be rejected. I know. So you go cry to your friends, then go out and do it all over again.
You're going to write another book someday (I hope, and if you're serious). So you may decide to query this publisher again. The rejection was definitely not personal. Don't burn your bridges. If you yell at everyone who rejected your first book--which, just maybe, wasn't the best thing you're ever going to write--do you really think they're going to take an unbiased look at your second?
Bridges. They are of the good. Don't set them on fire, or you'll have nowhere to go and you'll be dancing by yourself at the prom.
When you're dealing with a publisher, treat him or her like someone you want to date. Be respectful. Don't come on too strong. Present the invitation to the prom, but remember there are a lot of other people asking and don't take it personally if she declines your invitation.