Going deeper in into the meaning of the words & comparing, the word beautiful should be used when you want to describe a person whose impact reaches within. In other words beautiful is something which leaves an impression on the Soul.The word pretty is used to just describe how the person looks.
Pretty is something you are born with. But Beautiful, that is an equal opportunity adjective. -SearchQuotes
So next time when you use these words, be a little careful with what you really want to express. Also decide for yourself. What really you want to be-Pretty or Beautiful? You can be both. But if you choose to be beautiful, it will never really matter if you are pretty of not.The choice is yours.
The Awesomeness Quotient-If you want to know further how to be a beautiful person, STAY TUNED.