The first five pages of your story are going to make or brake you. Ever heard that before? When you are submitting to an agent or editor it's true. Here are a few tips to look over your own manuscript and beef it up before sending it out.
At the very least:
1- NO typos---get a bunch people to look it over with a red pen and listen to their feed back.
2- Good writing
The reader is who you ultimately want to impress so find a few people who read what you write and have them read and give their opinion. This is generally not your mom/sister/best friend. You need someone who can give you completely unbiased feedback. Not a "I love it! You are the best writer ever. There was nothing wrong at all. It was perfection." To make it better you need to hear about those weak spots. And every writer has them, they just fix it and move on. :) Remember that the creative process is revision.
Hook in your reader. Make them HAVE to read the next paragraph, have to turn the page, next chapter etc...
Find your voice as the narrator and stick to it. Do not let it trickle into your character's voice. People sound and speak differently and so should your characters. That lets your reader know who is talking even before they are told.
In every conference that I've been to the agents/editors said that they are just people who Really like to read and they are just searching for a new story that they love. So write for your reader and you'll do fine.