Patience. I believe that is one of the things you need to learn as a writer. That, and how to take criticism.
Once you finish a manuscript, you get so excited you want to query it immediately, but you can't! Oh no, no. That is a big, fat NO. Sure, everything sounds great to you, and you read it about a million times, but it's never complete until you get other opinions. After looking at the thousands of words for so long, your eyes start memorizing and skipping over things that others will catch for you. It's also important to have a Critique Partner to tell you to take out the word vomit you spewed all over the page just to add on a couple hundred words. Your CP's and Beta readers will tell you if your characters are realistic, if there's any plot holes, and if the story itself is any good. You have to be realistic. There will almost always be something wrong with your manuscript, whether it's a big deal or nothing but small grammar issues.
So far, I've been really lucky. My CP helped me tighten up DROWNING BAILEY, and let me tell you, it needed it. I had some wonderful Betas that read it over the last few weeks, and an awesome friend who offered to edit it for me. Seriously, I have some truly talented people in my life. (Thanks, Twitter!)
I used to think that when an agent says, "Please query when your manuscript is in the best possible shape," that it meant when you, yourself, have reread and edited it as much as possible. What a newb! As if I could prep a publish-ready-manuscript all by myself. It's all about having a team of friend's who are in the same boat as you, who understand you, and who support you the whole way. Everything takes time, and you have to be ready to sit and wait. This is a good thing. You don't want someone to rush through your manuscript as if they'd hardly given it the time of day. You want those people who are going to sit down, absorb your words, and critique it little by little.
Yes, I am anxious to get DROWNING BAILEY in the slush pile, but I'm thankful that I've taken the steps needed to make it as good as it can be. And you'll feel that way too. Just remember...patience.