Work back from what you need
Start with the income you want, add business expenses, then allow for taxes. Divide by the hours you can realistically bill, which is usually far fewer than you work.
Price per project where you can
Clients compare totals. A project price rewards you for getting faster and avoids debates about hours; keep an hourly rate for extras and changes.
Raise prices on a schedule
Plan a review every six months or when you're fully booked. New clients get the new price; give existing clients notice.
Do this today
Run your numbers through the freelance rate calculator and write your minimum hourly rate.