Why isn't my hair as nice as other girls' hair?

I wash my hair everyday and it frizzes very easily and it doesn't straighten well at all when I flat iron it. It can sometimes get greasy too. Am I doing something wrong? I use clarifying shampoo and I use the conditioner on the ends only just like what I've been told to do. I DO NOT put anything else in my hair other than hair spray after I straighten it. Is there something that I should be using to make it better or is it going to be like this no matter what? Oh fyi, whenever I get it done professionally by any stylist, it looks fabulous and how every other girls' hair looks, but when I do it myself...ewww...help please? What can I do about it?