Polish the package, not just the book
Agents ask for the same three things: a one-page query letter, a synopsis of the whole plot (ending included), and the first ten pages. All three must be as good as your best chapter.
Part two
There is no single right route to publication. There is only the route that fits the book you actually wrote.
Agents ask for the same three things: a one-page query letter, a synopsis of the whole plot (ending included), and the first ten pages. All three must be as good as your best chapter.
Send eight to ten agents at a time, chosen because they represent books like yours. Wait for responses, adjust the letter if nobody bites, then send the next batch.
Watch for rights grants, reversion clauses and option terms. A legitimate publisher never asks you for money.
A developmental or copy editor, a cover designer who works in your genre, and an interior formatter. The cover sells the book; do not draw it yourself.
Build a small mailing list, line up early reviewers, and publish. Then start the next book — a backlist sells the first one better than any ad.