You are so young.. Please stay safe.
Right now you need to read as much as you can, here is some things that can help:
http://sexworkerhelpfuls.tumblr.com/resources
second of all, you are what they call barely legal, so use that to your advantage and don't sell yourself short. clients would pay more than what you are asking. IMO
Don't do what you don't want to do, don't let these clients tell you that you have to do something that you are not comfortable with, it is your body and you business., learn to say no if you don't feel comfortable.
Don't think you have to take all calls, learn to screen these men.
Always use protection (condoms that you buy)
Don't use your regular phone no. get a hobby phone.