I can not sleep with a TV on, unless I'm absolutely desperate for sleep.
That, or I have a laptop on with me, or even just browsing the web on another device (iPod, PSP, etc...) which tends to keep my with something to do for a few hours.
Once you get older, you'll find it's easier to do, wether because you literally have to stay away awake because you have no time to sleep, or because you just feel like staying up. Oddly enough, with the ability to stay awake for longer, you'll also gain the ability to sleep for stupidly long times that you actually don't need. Like, going to sleep at midnight and waking up at 3pm or longer.