So should you cut your hair yourself? Should you be cutting your hair yourself? I would say no, don't do it. Nothing is better than a professional doing it.
But if you really have to, there is one thing, with long hair, that you actually can do. It's one chop. So I'm going to show you.
You will need to take all of your hair and actually brush everything. So it's brushing or combing everything forward. Then go all the way to the end. And what happens here, you will take the scissor and just cut that straight off. What that will do is actually keep all the length that you have here, that goes here. So that won't be touched. And once you cut here, it will actually give you some of the layers in front too, at the same time. So in one shot you can actually make your hair look pretty decent.
The second option would actually be to turn your face sideways, comb your hair in the front, meaning bring all the hair towards you, and actually cut the bottom of it in a straight line. And do the same thing on the other side. That's the only way you can actually reach the back of your head. It won't be perfect, but it will help.
But, like I say, nothing is going to be better than the professional. So don't do it yourself.