It's a great idea to figure out how much you're going to charge your client before your client asks you how much your charge... that way you can avoid that deer in headlights look that clients find unsettling when hiring a professional.
There are 2 ways to charge: hourly and per project.
Hourly pricing is easy. You pick how much you want to make in a year and divide it by 1,000. That's your hourly price. You want to make 100k? Charge $100 per hour. You want to make 254k? Oddly specific, but ok, charge $254 per hour.
Per project pricing is... not so easy. You have to scope out the project in detail, estimate how many hours it's going to take to do the work, pad that number to account for the fact that you have no idea how long anything takes, and then get it all in writing so that the scope of the project doesn't balloon out of hands.
In my experience, per project pricing is ideal if you like arguing with your clients over what was included in the price and what isn't.
I like peace of mind and getting work done over stressing out over scoping out projects and arguing with clients, so hourly works best for me.
I charge a premium for hourly work, and offer slight discounts for monthly rates when taking on larger projects. I also have a minimum commitment amount, and only work on retainer or with a credit card on file.
Try it and let me know what you think!