Do your homework to cut down on rejections on your part. You should have gone through Writer's Market 2009, Jeff Herman's guide to book publishers, editors and agents, Preditors & Editors, Agent Query. Very important, always match the correct genre. It would would be a hugh mistake to send a romance to an agent/pubshier that only handles mysteries, but you won't believe how often this happens. Now the fun part let's all play are favorite childhood game, Simon Says, remember if you don't do what simon says you're out, only this time you'll get a cute little rejection letter for not listening. Agents and publishers are human too, they are overworked, have families and friends, and most of all if you've never been a New York office you would freak to know the stack of submissions really are piled to the ceiling on their desk. Yikes! Even with the perfect manusript these things will make the best agent/publisher throw you manuscript in the slush pile.
Read the entire submission guideline for the agency you are sending too. Don't get cute and pull any tricks like color paper, going through three boxes till you get to the manuscript, ...you get the idea.
1. Font: Always use 12pt Times New Roman/Courier
2. Use good quality paper, speaking of paper never use paper clips, staples, or fold paper. make sure it's clean, i.e. no coffee stains, or cigerette smears.
3. Use a lazer printer, if you don't have one , get it copied at Kinko's or any office supply store. Unless you want immediate death never sent a hand written, or copy where your printer has run out of ink getting lighter in the last few chapters. sudden death for sure.
4. Spacing, Typos, and Margins: Check the submission guidelines/call to confirm. No cute stuff follow the rules. Some companies now are having authors use only one space between words so check guidelines. I know this sounds like I'm beating a dead horse but I'm not. Note if you work on one computer say, and send it to another for rewrites, the back and forth tends to cause formatting issues, you are better off to stay on one computer. I see this with say your work is on an old computer with XP and transferred to a new computer with Window's Vista.
5. As I've written before, but worth repeating:
Start in the first chapter in the middle of action, you should have action/heat on every page.
Use Dialog, Show don't tell
Back story is a few sentnces, anymore and it's not a back story. Salt & Pepper the back story through the book, don't hit the reader with it all at once, they'll loose interest and the book will loose speed.
Conflict is king! use it, abuse it, and anything that does not move your story along cut it!
Your ending should be as strong as your opening, don't wip out now, Nail it!
6. Run the spell check, but remeber the word may be correct but the the right meaning. Use Explanation points, ..., dialects, slang, sparing. Remenber to use a good word mix, Watch you POV, your repretention one one word, watch for purple prose.
7. Rememer when writing the scene to sift the five senses through the character. i.e. What is the characrter feeling, seeing, hearing, smelling, touching, gives the scene a real feeling.
Hope these tips were helpful Happy Writing!!