I find that the most effective way to beat out your laziness is with good personal health. That means regularity in your consumption and exercise. Maybe you'll all disagree with me, but this is what I found to be effective:
No CAFFINE! God, I see so many girls (fine btw) walking around with a latte in their hands @ UCB. it's horrible, it's an addiction. Once you get off you get into caffine withdrawl with the whole headaches and sickness.
Earlier to Bed. Set study hours that you always follow week after week. Try finding a certain place too. Clump lectures together (personal preference, I got from 8-12 5 days a week). Call me psycho, but I wake up around 5am everyday, either to catch up on HW, lectures, notes etc, or just to enjoy my morning by reading and drinking tea (probably just as bad as coffee)
Eat good stuff, Bananas! Who here likes that? Potassium to get your nerves working. Good fiber for crapping and digests well with anything. Eating healthy really really really helps! You'll find yourself with more energy and looking better too! (went from 180 -> 140lbs).
Listen to instrumental stuff, without lyrics. I can't be listening to Iced earth or black sabbath when doing HW. Lyrics and erratic music really disturbs me. I also found myself more focused around something with a subtle yet consistence noise (IE small stream of water flowing by a creek) I usually listen to classical things or instrumental scores (Kenshin OVA!)
Join a sport! I'm doing crew to keep myself fit and focused. Maybe it makes me so tired that I can't think about not wanting to do HW, but something with intensity really helps my mind focus.
Meditation, read a time article recently about it and i've been doing alittle recently (but don't dooze off and sleep, once woke up in th emiddle of the night on some random grass lawn)
Honestly, motivation isn't something you can really muster without help and much personal development and honing of your habits.
Anyways, hope that helps someone premed or not.