Have you thought about what your publishing outcomes and hopes are, and about your potential market?
Have you considered self-publication and started a website to self-promote?
Have you read and re-read your manuscript and self-edited it to the best of your ability?
Have you run a basic spell checker?
Perhaps you have had a manuscript appraisal or beta read from a critique group? Have you considered everyone's constructive criticism to transform your writing and get it in the best shape it can be in before you pay for professional guidance?
Have you signed up to Twitter, Facebook, writing sites and forums?
All of these things are worth thinking about as you take your first steps towards publishing success. Remember, editors will figure out the cost of editing your book based on either a page rate or how many hours of work it will take them. The longer the novel, the more it will cost, so you can keep editing costs down by doing some simple checks yourself and editing to remove padding.
Even if you have done all of the above, having your manuscript professionally edited will take it to the next level.
Before authors hire an editor they should:
Check for common errors
Assess characters carefully
Examine plot and pacing
Polish first and last chapters
Let beta readers/friends/family read the manuscript