The Martini Method or Rewarding Task Completion
As a parent, I'm regularly offering carrots in exchange for the things I want my son to do. If you put your toys in your toy box first, you can watch your favorite show; if you read me this book first, I'll play that game with you, etc. In most cases, this is a great way to get the results you want without having to butt heads in the process.
This same methodology also works for self-motivation, if you're willing to stick to the requirements you set for yourself. While I love what I'm doing most of the time, there are days where my projects seem somewhat tedious. To get past it I set similar rewards for myself. Finish editing that how to video and you can play Xbox games for the 30 minutes it will be encoding is a common one. For bigger projects, like the ebook I'm currently working on, I break the project down into smaller chunks and reward myself for completing a new chunk.
A more famous example of this is the Martini Method used by A Clockwork Orange author Anthony Burgess. Burgess was a prolific writer, supposedly penning 1000 words a day every day of the year. Upon finishing his daily word count, Burgess rewarded himself with a Martini (or three) and relaxed for the rest of the day. While I'm not advocating being a functioning alcoholic, there's method to this madness in getting what you need accomplished while still enjoying the things you love. Shane over at Academic Productivity talks about the Martini Method in more detail, along with several other ways to tackle large projects. He frames it in the context of completing your PhD, but you could easily apply the process to any large project in your life.
If you've got your own methods for completing tasks, feel free to share them in the comments.