Take your time.
Don’t be afraid to take longer than you expected to move through the publishing process. It’s more important to get it right than to do it quickly.
There’s no such thing as a writer who can copy edit, proofread, design, and promote their book all by themselves. Unless you’re some kind of publishing superhero, you’ll need to get help.
Don’t hunt for deals.
Editing, proofreading, and design are all skilled trades and there’s a reason they’re not cheap. Cutting on costs will only leave you with distracting typos and a cover that won’t sell your book the way it should.
Shop around and do your research.
Don’t settle for the cheapest option or the first supplier you see. You’ve likely poured a lot of work into your manuscript. Make sure you find the right people for the job.