One of the most important things to make sure of when you're submitting to a publisher or agent is whether they actually accept what you're sending them. That might seem like simple common sense to most of you, but believe me, there are times when authors just don't seem to do their research.
As I mentioned in my post on February 27, every publisher and agency I know of has submission guidelines. You might have to search for them or ask other authors who are with that company/agency, but they do exist. In some cases, each individual agent in an agency has their own guidelines.
One of the most important components of those guidelines is usually what type of things the publisher or agent accepts. That's assuming it isn't completely obvious from looking through the list of authors the agency represents, or the book catalog of the publisher.
(And if you haven't looked at that list or catalog, why are you considering that agent or publisher?)
Sometimes it's even obvious in the name of the company what they accept.
And yet I've heard of adult romance publishers receiving picture book manuscripts; agents who only represent speculative fiction receiving contemporary chick-lit; and children's publishers receiving manuscripts with adult characters and X-rated scenes.
Assuming you plan to submit to a publisher or agent, and assuming you've already done your research on whether the companies/agents you're considering are legitimate, the next step is to make sure they actually accept what you've written. Some authors get excited about their story and the prospect of having it published, and send out query or manuscript "blasts" to every place they can find contact info for, without even paying attention to what that publisher or agent works with.
I know none of *you* do that, right?
Once you have your list of "I want to submit to them" ready, take time to visit each site. Make sure you completely understand what genres, categories, age levels, etc. they accept. If the site and submissions guidelines are unclear, you should be able to find an email address where you can ask for clarification. But don't just assume that because you really want to work with that publisher or agent, they'll look at what you send them. If it doesn't fit what they usually work with, they might not even bother to read your submission.