How do I...............?

How do I get myself up earlier?!?! Okay I'm a 16 year old girl and I CAN'T seem to get myself up early enough! This morning I set my alarm clock for 8 since it's summer holiday and I don't usually like sleeping till 11 or 12. So my alarm went off at about 7:45 this morning, and I didn't hear it!! It's an old fashioned alarm clock, the metal kind with the bells and everything and it was going for like 20 minutes and I slept right through it!! My mum had to come in and tell me to turn it off! Okay so my real question is, is how do I make sure I can get up early and on time and not sleep through my alarm?? School is going to start in a month or so and I want to start training my self to get up earlier. Any thoughts??? xxx