As a publisher who frequently receives many manuscript submissions from writers keen to seal that first publishing contract, I am always amazed how the vast majority are prepared to give their dream as little chance of suceeding as possible.
Give your manuscript a chance!
The first very simple thing for any prospective submitter can do is read the publisher's submission requirements. Many state if they receive any submission which does not meet these then guess what...yes the very first door is firmly slammed shut! Remember no two publishers are alike, if you intend to submit to more than one then make sure you go through the protracted process of following all criteria for each one correctly.
The next is grammar. Any manuscript which is not polished grammatically is very quickly discarded. The storyline hidden away amongst the errors will be lost and forgotten. Gone are the days when publishing houses would support the long journey editorially of even the most exciting submission. The costs can be prohibitive.
Next, is what I call the 'X-FACTOR SYNDROME.' Utter delusion to the quality of storyline, plot, dialogue and character which sees the writer send in their manuscript with an overblown sense of grandeur. A covering letter which extols to the publisher that within in his hands he now holds the next 'Potter.' It will make me millions is the cry, oh and of course you! Now it may well be the case...but let the publisher make their own mind up about the quality of what they hold. That is not to say that you should not portray your manuscript with a level of excitement which portrays your enthusiasm for your work, but leave it at that! My advice which I believe is invaluable to your quest, is to get your manuscript critiqued. A review of the strengths and weaknesses of your work from a professional point of view is a must. The cost will pay dividends in the long run.
Simple things to be on any submitting to-do list are if submitting by post ENSURE you have supplied a stamp addressed envelope. Make sure you have looked at the list of books which the publisher has published, this saves you so much time, effort and money. No point sending a crime thriller to a publisher who is not interested in publishing crime thrillers! Try and get an agent, not all publishing houses will accept unsolicited submissions and will only consider work through a literary agent.
But this leads me to the most important advice for any writer wishing to receive that holy grail through the post or as an attachment on their email, a publishing contract. Give the smaller independent publishers a chance to consider your work, they tend to be more flexible in accepting submissions that are unsolicited. Do not restrict yourself to what being published actually means and the opportunities today brings. A book published through any format by a publisher who has signed a publishing deal with you, means you are a published author!!
It is a great feeling, do not hinder any chance you have by not getting the basics right.