#1 Pick the right music. Fast, fun music makes all the difference if you want to run. Find a mix with your favorite, upbeat songs and I bet it will make a huge difference not only in your speed but your endurance.
#2 Watch T.V/Read/Or at least work out in front of a mirror. It's boring to run at a blank wall. It is. I'm sorry. If you can manage to watch tv or read, the time will pass a lot easier. But even better, if you can position the treadmill in front of a mirror, you can watch yourself run. Seeing yourself run is motivating. You can see your form and perfect it. You can even see how strong you look, and that's pretty motivating.
#3. Do more than just run. You can really mix it up on the treadmill. I dance on the treadmill. I skip, I run, I walk, I go backwards, sideways, and make up crazy moves. No one said you had to just run monotonously. It CAN be fun!
#4 Mix up your speed and incline. In all workouts, pushing yourself is good for your body and mind. Even more so on the treadmill. 45 minutes at 6mph is okay. Boring. But okay. Why not run for a bit at 9mph. Then go back to 6. Then go to 8. Then go to 6. Then 10. Then 6. You get the idea. And who said you had to walk on a flat surface. Try it at all different inclines. All in the same workout. Whatever! As long as you're still moving and sweating, you're still getting a good workout! Maybe even better if you're running sprints and getting solid HIIT intervals.
#5 Set a goal. Again, running for no reason while staring at a wall is boring. If you're running to get somewhere (metaphorically, since you will be in one place, lol) it's a lot more interesting. Try to beat your last distance and/or time. Follow a 5K training schedule or specific treadmill workout. Set a goal to run for 5 minutes straight. Then 6, then 7.... Just set a goal. And kick that goals you-know-what. It feels good to win!
#6 Strengthen your legs. Building your leg strength makes you a better runner. And do you know how much more fun it is to be able to run really fast? Yeah, it beats the crap out of struggling a long.
#7 Take a break once in a while. If you get on the treadmill a couple of times a week, take a break. Do something else. Yoga, Pilates, Spinning. Even a walk outside! Mix it up. Your mind and your body will thank you!