Rewards, mostly. I keep a small stash of food treats (mostly chocolate, but sometimes if we can afford it some fruit like pineapple too) and a healthy list of movies and tv shows I want to watch.
Every task I know I'm not going to enjoy working on I break down into as many small parts as possible. I'll use the example of doing NaNoWriMo every year, where the goal is to write 50,000 words in 30 days that roughly equates to 1,667 words per day. To stay motivated I break each day down into 4 parts - 3x 500 words and 1x 167 words. For each 500 word section I complete I allow myself one small food treat or a single episode of a show, and after completing the final work section of 167 words I have all 1,667 for the day and treat myself to a movie or a few episodes of a tv show.
Knowing that I have such a thing to look forward to keeps me going and if it works I'm not going to question it :)