I know others have said this, but:

Be picky.

You have done your work. You have written a book. If it is a good book, it has value to every publisher that publishes in your genre.

Start high. You want to best possible deal for the work you've done.

Experience for authors is not like experience in other industries. There are, in fact, advantages to being a debut writer (e.g., you could be a star + your advance is going to be cheaper). There are also advantages to having an established sales record. But these things determine how much you'll get paid by legitimate publishers. If a publisher is in any way sketchy, you're better off passing. You have the property people want. It is far worse to be published badly than not published, because being published badly leaves a negative trail (poor sales, poor PR, poorly edited books).

Start high. Look for agents, too. Then work down your list. While you wait for responses from the best agents and publishers, write another book. This will help far more than just about anything else you can do. When you get to a certain point on your list, trunk Project #1 and start sending out Project #2. Do not waste Project #1 by sending it to dubious agents or publishers. Not only will it leave a trail, it will also burn your rights to Project #1--rights you may want if Project #2 goes on to sell big.