There are many online resources of other crafters and their experiences in pricing their items for sale. You can also do a type of "market research" to see what other people in the same field as you are selling things for. When you make something that is well done and thought out you can honestly expect to be able to sell it. (This does not mean your very first project may be worthy to sell, in my case the first 10 things were terrible and instead gave them away as gifts to my children who loved them.)
Grab some books from the library, buy books, read some more! There is never an end to learning so be sure to use the resources that are at your fingertips. If you like a favorite blogger or artist you know, ask them questions. I love getting questions from my followers and enjoying teaching others from what I've learned.
When you find a formula you like try it out! Yes it may not work the first time, or work in the long run, but you won't know until you try it if something will work out. In my example I started by just guessing at an item's worth and on what similar items like mine were selling for. Then I moved on to using the item's dimensions and a pay rate scale to figure it out, which worked fairly well.
In the end I chose to go with a formula from one of the Etsy blogs, and using that I discovered I was underselling myself by almost 50%. Here is something important to remember, when you are first starting out it is ok to sell your items for less. As you mature your craft and get better and faster I believe you can charge more for your services.
The new formula I am using is: Materials + Labor + Expenses + Profit = Wholesale x 2 = Retail
Here's an basic example and we'll use 10% Profit:
$3 + $4 + $0.50 + 0.75 = $8.25 Wholesale x 2 = $16.50
One of the things I hadn't even considered is the difference between Wholesale and Retail!
I network with people from all sorts of careers and have been asked for large quantities before, now with the way I will handle my pricing now I have the option to give them a great offer, without cutting into my profits so I make nothing, or my other expenses.
You can find the full blog here at Etsy.com and they do a whole breakdown on what each section contains.
SEEK GOOD ADVICE
Whether it's Ravelry, Craft World, or Etsy seek out the advise of other crafters when you come up to something you can't solve yourself. This is what I did. I wanted other sellers or buyer's opinions on how much they thought was fair to charge and why something may not have worked. Often what you will find is that they will see it from a different perspective you might have not even thought of! Once you have this advise decide what you are going to do. It is your choice in the end, now that you've heard from others you can pick!
I know I will never stop learning, which makes me excited for all the possibilities in the future. So keep an eye out for the neat things that pique your interest and learn about them! You might discover a new tool, idea, or even a project!