Credit and credit card help!!?

Hi i am 19 years old and currently have bad credit. I got credit cards and just charged so much. Since then i consolidated my bills and i am paying a payment every month (never missed one payment). i am also leasing a car and its in good standing. My credit scores go from 450-600 (horrible). How do i fix this before i really need good credit. I cancelled all but one credit card. Will these mistakes haunt me forever? What are some ways to improve my score. Thank you for the help