I typically try to get workout videos whose workouts are 20 mins- a half hour but higher intensity. That way I literally have no excuse not to do it. For the first two and a half weeks of diligently working out, I struggled with motivation, tried to find excuses for not having enough time, but I also saw it as a personal challenge and I did not want to fail. After three weeks, I began noticing that everything they say about exercise is actually true. Especially that part about getting a kind of high off the endorphins. Now I don't dread the exercise as much because I look forward to the happy endorphins that course through me after.
It also helps to have a fitness buddy to keep on your case and nag you. :-p