When hunting for an agent, you're bound to hear that dreaded two letter word a few times. While it's true that not every book can be right for every agent, no matter how well it's written, there are things you can do to increase your chances of getting requests.
Polish that query.
Remember all that time you spent making your manuscript sparkle like a vampire in the sun (well, certain breeds of vampires)? A query gives you around 500 words--usually less--to introduce your main character and the major the obstacle they encounter. All with dazzling amounts of voice and excitement. Don't take it lightly. You put countless hours into your book. Don't rush to query with something less than stellar.
Check in at Absolute Write's Query Hell. Read the stickies at the top about query writing and read through some posts that have already been critiqued. Many mistakes critiquers point out are common ones you can fix on your own. Once you're ready to ask for a critique yourself make sure you stick around and offer your help as well!
But really research them. Just because an agent is open to submissions, it doesn't mean they're the right match for you. Most post the specific genres they're looking for and some even include wish lists that detail what they're really hoping to find. Look up the agent's past sales as well. If they recently sold something that's very similar to your own book, they're more likely to pass simply because it could create a conflict of interest promoting two similar stories. Of course this doesn't mean you should rule the agent out entirely. It's only something to keep in mind if they decide to pass.
Follow Submission Guidelines
Agency websites give specific instructions for querying and failing to follow them will insure an automatic delete. Some ask for the query and sample pages pasted into an email, while others accept attachments. Also be sure to see if you query the agency or the agent directly. If you're querying a specific agent, you'll want to address the query (in a businesslike manner!) to them.
Speaking of Sample Pages . . .
If your query sparks some interest, the sample pages are where you need to bowl them over. These need to be free of grammatical errors, intriguing, and well-written. Take the extra time to make sure the sample pages are the absolute best you can make them.
Agents are busy people and they're human just like the rest of us. Queries will be eaten in inbox folders from time to time. The best way to make sure you don't miss an opportunity at a great agent is to keep yourself organized. Try using a spreadsheet listing agents you queried and the date you sent them off. If the agent responds to all queries and it's past the time window they give, wait a few more days then send a follow up. However, if no response means no, don't badger the agent with more emails.
Bonus tip (because five just sounded more well-rounded than six haha)
When you're sure your book is ready to be sent out, it's nearly impossible to fight the urge to hit send, send, send. But try not to query more than a few agents at a time. Send out four or five queries and see the results. Were they all automatic R's? Maybe it's time to revisit the query and see if you can polish it more. If you got some partial requests that turned into R's look over the sample pages or consider any thoughts or notes an agent might have passed on.
It's a hard truth, but the road to publication is filled with rejection at every step of the way. Remember, you only need one yes to get your shot. Don't let querying be something scary. Put in the time and give yourself the best chance you can.