It's critical that you first identify *why* you're procrastinating, because procrastination comes in many forms for most of us, and, depending on the form, the ideal solution is different. See if any of the following statements resonate with your situation:
1. The task I need to do is boring and uninteresting. I'd much prefer to do something else.
2. I don't see the point of the task, I will not feel any reward in completing it.
3. There's something else really exciting in my life and I'd honestly rather be doing it than anything else right now.
4. I know this task is going to be very taxing (physically, mentally, or emotionally)
5. I fear that I may not be able to successfully complete this task.
6. I have trouble articulating why I'm unable to get rolling on this task; no rational explanation seems to explain my hesitance.
For many of these cases, the answer lies in discipline. It's not fun to think about, but cultivating self-discipline is perhaps the single most powerful way to get more out of your life. If you felt that 1, 2, 3, or 6 applied to your situation, it's highly likely that you would benefit from cultivating discipline. I won't write a manifest on how to do so, as there are heaps of information out there on the subject, but basically, strengthening your discipline comes down to strengthening your ability to control...yourself! Enough mental discipline will give you total control over your mind and actions -- by that I mean, you'd have the ability to 'just do it' in spite of disinterest, lack of reward, or presence of strong distractions. You would simply 'override' those feelings. Many people will say 'just do it' without recognizing that this process of overriding our primitive emotions and desires requires a certain 'level' of discipline, and that those without it can't 'just do it.' Being able to just do it is about growing your self-discipline. So for now, I recommend just a tiny bit of procrastination in the form of doing a bit of research about discipline, willpower, and how to take concrete steps to help yourself procrastinate less (without having to 'just do it' all at once). Cultivating discipline and willpower in, even in small ways (like not having a cookie you dearly want, or forcing yourself to do some extra practice problems in your school textbooks) will accumulate over time to give you the control required to stop procrastinating in those particular contexts.
As for 4, the best I can recommend is to ask for help from family or friends if applicable, if not, consider asking for a friend to just hang out with you while you do the task, acting as a shoulder to lean on. It's likely that you've overestimated the task and underestimated yourself, but if you need reassurance to get through, just working *in the presence of* (not necessarily 'with') others can do the trick.
Finally, 5, well, this is rather easy. Whether or not you're capable of completing the task, procrastinating and believing that you can't is sure to cement the negative outcome into reality. On the other hand, zealously pursuing the task with optimism and a strong belief that you can succeed gives you the highest probability of doing so. My favorite quote of all time is from Henry Ford, who said "whether you believe you can or you can't, you're right." Elegant way to put it :)
Hope some shred of this ends up helping somebody out there!