As everyone else said, and I agree, one of the worst obstacles is talking yourself out of it and trying to come up with self-justified excuses not to do something that you truly, internally, know that you need to do. I still have a problem with this--I will never not have a problem with this--and it's really hard to teach someone to just "develop willpower". It's a strategy, and you have to learn it.
Tell yourself why you're doing something, and remind yourself constantly. Try to think in the bigger picture, if you can. Instead of "I'm going to class because they take attendance", you could think, "I'm going to class because I'm paying thousands of dollars for that damn chair and so you're damn right I'm going to sit in it!"
I, personally, like to think about how by getting things done now, I'm making my life easier in the future. If I assemble my backpack and set out clothes the night before, I have more time in the morning to get ready and move at my own natural pace. If I get my homework done during the week when possible, I'll have more free time this weekend to do whatever I want. And then when that time comes, and I'm playing video games on a Saturday instead of doing yet another 40-page dry as hell academic reading, I think to myself, "You're the best past me. Always lookin' out for me. You know what's up." And I revel in the rewards that I reaped for myself.
A little bit of an anecdote: In 8th grade, I did not care. About anything. I joked with one of my friends once that "my F is a better F than your F." I was failing every class. It wasn't because I wasn't smart. Hell, it wasn't even because I was lazy. It was just pure apathy and a lack of willpower.
The solution that changed me? Finding my drive.
I did not find that drive by myself. I did not have to go out looking for it. In my case, it punched me straight in the face and woke me up.
The principal and many of my teachers pulled me aside and had a sort of intervention-style meeting. I was told that if I did not improve my grades, I would not be graduating in a few months.
This was eighth grade! I was sure as hell not about to get held back and watch all of my friends move on to a completely different school and leave me behind. Within one week all of my F's had skyrocketed to C's. I graduated on time, with my class.
This did, however, also have a negative impact on me. I went overboard with my drive. I was so impacted and shaken up by the potential negative effects that to this day, I'm still not at an equilibrium. My obsession with perfectionism has been so extreme ever since entering high school after almost being held back that I will cry over a B. I will think to myself, "Why even bother doing something if I can't do it perfectly?" That's dangerous thinking that threatens to bring me right back to square one. But I recognize this, and manage to keep my willpower in check.
My sister, who struggled academically, once asked me "how I did it." When I asked what she was talking about, she said she was referring to the anecdote that I just shared here. My response was that I just had to develop the sheer willpower to crawl out of the hole I had dug for myself. There is no way to force someone to develop willpower if they are unwilling. There is also no way to tell you how this willpower will manifest, as it is different for everyone.
I would take everything one step at a time. Try to find your drive. Mine was more obvious: I didn't want to get held back. But now that that's no longer a threat to me, my new drive is something more along the lines of "making my life in the near future easier by getting my shit done today." Yours may be different, it may be the same. I'm not sure. In the end, you're the only one who will be able to figure that out, if you find it useful. But when you do, it will be a helpful tool for navigation.