The advice that I keep giving people is this: Write a new, different, and better book. Go to the bookstore. Find books on the shelves that are similar to yours. Find out who published them. Get those publishers' guidelines and follow them to the letter. If the publisher says "no unagented manuscripts" get an agent. Find out who agented those books you saw. Get those agents' guidelines and follow them to the letter.

And while all this is going on, write a new, different, and better book.