As with anything else, you need to know how to do it. That means you will need to learn by taking acting classes.
I also recommend that you start to understanding how the acting industry works. Start reading some of the trade papers like Back Stage or Variety or Hollywood Reporter for example. You'll learn a lot.
Also, pick up an acting technique book or two, like Sanford Meisner On Acting or The Art Of Acting. They will help you see what classes are like and help you understand what it is you can learn in them.
Then, you will need some business skills that will help you to be able to get your talent notices. For me, this comes before getting an agent.