What are good ways to improve sketching skills?

I'm 21. I am just strating to develop my drawing and sketching skills and I have been using the aid of the internet, especially youtube videos to learn about the technicalities of sketching. I'd very much like to sketch beautiful portraits. I believe that I am inclined to the arts and that I am innately a creative person. However, whenever I try and draw I just look at my work and feel that it looks awful. I'd like to sketch face with precision, I dont want to sketch britney spears looking half like herself and half like an ape.. Please help me!