This is a question a lot of people ask. What should I charge? What am I worth?
If you've done any research, you'll probably realize that there's no one right answer. A combination of what you do, your skill level, and your client all make up an ideal rate for a project.
An hourly rate
The first thing you need to do is figure out what you feel is a good hourly rate. Maybe this is where you're stuck. That's ok, we'll work through it. What you first need to consider is: how much would you like to reasonably make? If you're just starting out, the best advice is to follow your gut. If $50/hour seems too high for the work you can deliver, maybe it is. If $30/hour seems a little low, again, it probably is. You have to consider that as a freelancer, you're no longer getting health benefits. You no longer have the guarantee of a full-time job offering you 40 hours a week. No sick pay and no vacation time. And don't forget taxes, which as a self-employed person, you now have to pay more, around a third of your income. You are also, theoretically, a specialist in your field that is being hired specifically for those skills. Maybe $50/hour isn't so crazy after all. (Maybe after considering everything relative to your skill level, $100/hour isn't so crazy, either.)
The next thing to consider is: what is your bottom dollar? If someone hires you for $20/hour, booking 50 hours of your time will only cost them $1000. Charging too little will sink you. You'll get bad jobs and they will take up too much time. If you're dedicating all that time to one underpaying client, you won't be able to pursue other work, take on new projects, or have any time away from work.
Generally speaking, I try to avoid taking on projects on an hourly basis, and I'll discuss why below. Ultimately, this number should serve as your baseline. If you are consistently getting work and getting better, start to raise that number. After a year, give yourself a raise, just like any other job. If you have stuck with freelancing for a year, you've definitely learned a ton of lessons and should have almost certainly increased your skill level.
You might make some mistakes on your first few projects. We all do. You may charge too little, or they may just not turn out very good. That's nothing to be afraid of, it happens. But if it feels like you're not making what you are worth or are being taken advantage of, you probably are. The best advice I can give is to wrap up those projects and go your separate ways. Once you get a feel of how much time you're putting into work and how much you're coming away with each month is when you can make a truly informed decision on how much you should charge.
Your skill level
This is the big question mark, especially when starting out. How good am I? Can I do what they want?
You should have some idea of what you are capable of and what you can deliver. You will make mistakes and learn new things along the way. Some projects won't go as well as you had hoped, but hopefully that's a small number in comparison to the bigger picture.
This is the single biggest thing that will increase your rates. If you're a web designer, come up with some personal projects you want to pursue, or make a website for a friend or family member. If you're a videographer, make a short film with your friends, or just go film around your town. If you're a photographer, you have no excuse to not be taking pictures every single day. Make mistakes on these projects so you'll make less on the big ones. You'll learn about design, lighting, audio, etc.
As you have better projects in your portfolio, your value becomes more obvious. Sprinkle this in with some client work and you'll soon have an impressive website. Bigger companies and opportunities will come calling.
If you're not sure you're ready for freelance work or don't feel like you can charge a fair rate yet, this is even more important. Do as much as you can to improve your skills. Read, consume work from those that inspire you, and get involved in some communities built around your craft. As you get better, people will start noticing your work. Maybe a successful freelancer will bring you on to help out with their project when they get too busy or need more help. I know I've done this multiple times. This will build relationships and suddenly you have someone you can trust who you can just ask: "Hey, what should I be charging for this stuff?"
Freelance project rates
As I said above, I like to book projects on a flat rate rather than hourly. This can be a rate per day or for the entire project.
One reason is that it's much simpler. As you take on more work, you'll get a better idea of how long it takes you to complete a task. You'll also get better as you repeat those tasks and come up with systems for your work. You shouldn't be punished for working quickly, after all, your client should be paying for your experience as much as the labor of your services. Estimate how long you expect a project to take, including things like meeting times, travel, and revisions. Come up with a number based on your comfortable hourly rate multiplied by the total time you expect to take.
If you do this, then you're not tracking every minute in a spreadsheet or on paper. There aren't questions about if time spent on phone calls are charged by the hour, because they should be built in to your flat rate. A 15 minute phone call might not seem like it's worth charging for if you charge $40/hour. If your client makes six 15 minute phone calls over the course of a project, that's suddenly an hour and a half of your time that you didn't get paid for.
I base my day rate on 10 hours. On some projects, a day may be 12 hours, others it's 8 or 9 hours. You'll feel this out as you get more work.
Another advantage is that it's easier to manage your schedule. If someone hires you for 20 hours of your time, they may need two hours a day for the next 10 days. Or, you could say 20 hours is two full days or four half days, and that you'll exclusively work on their project between these times. I've found this to be really helpful during revisions. When I say, "Ok, I've blocked off 10 hours on Tuesday to make any necessary changes, I'll need all your feedback by then," things are much more organized than if I add one bit of feedback on Friday, get more on Monday, add it, more on Wednesday, and so on.
In the end, you might be making what you made if you charged hourly. Occasionally, you'll make less. This can suck, but it happens. The lesson here is to be very clear up front about your services and terms. Usually this happens when tasks continue to be added to the project, it wasn't represented correctly, or you just miscalculated. The first two issues can be resolved with a clear contract. The third, you'll just have to learn for the next time. To avoid this as much as you can, be clear not only about the terms, but also what any extra charges may be if, for instance, there is an extra set of revisions. As long as the reasons for another round of revisions aren't you fault, the client should understand that it's outside of your original agreement and be ok with paying you for the extra time.
The magic with charging a flat rate, though, is that on some projects, you may make more than your normal hourly rate because things went smoothly. That's great, because if things went well that means the client should be thrilled. Guess what? They no longer care if they just paid you $100/hour. You totally wowed them.
So, what should I charge?
Sadly, there is still no exact answer. Hopefully some of my writing has brought up points you didn't consider, or maybe didn't consider strongly enough. Like with all areas of freelancing and creative work, a large part of it is following your gut and listening to your head. If you keep thinking you should be making more money, you probably should. If you're afraid you can't offer good value, you may want to proceed with caution.
Figure out a good hourly number. How many hours do you want to work to make a living? Figure out how many projects you can reasonably take on, and be smart about scheduling out your time. Improve your skills, hone your craft, and maybe even focus in on a niche market. As you can better serve your clients, you can ask for more money. It's a process, and with some practice, you'll figure out what works for you.
(Disclaimer: I shouldn't have to say this, but here it is anyway. If you need financial advice, you should always seek out a trusted, professional financial advisor. I am not one. I am simply sharing some practices that have worked for me as a freelancer.)