I spent weeks studying the publishing industry before I sent out my first query. To this day, even after having published my 1st novel, I still look for new information on industry trends. I pay heed to the advice given by agents on there blogs (even though I don't, as yet, have an agent). For those seeking to get published, the best advice I can give you is to spend time studying the industry [publishers, agents, query letter writing etc]. If you are that set on publishing your manuscript, invest time in learning every aspect. One last thing, always be professional. Don't bash an agent or publisher that rejects your manuscript; thank them for their time and move on. Rejections are not meant tio be personal - don't take it so. My book was rejected 7 times before I found a publisher. Sending an email or letter to those who rejected the book [in order to bragg] doesn't say anything about my writing skills. It just sends the message that I'm immature and unprofessional.
For additional advice in this regard, check out the blogs of agents spread accross the web. These sites and their respective agent provide valuable bits of info to help you along.