1. Make it nonnegotiable.
Don't tell yourself that you can cop out.
2. Make it actionable.
Be clear about what you're going to do to reach your goal. For example: "I'll go to sleep 30 minutes earlier so I can wake up and exercise in the morning."
3. Set a deadline.
Mark it on your calendar.
4. Schedule it in.
Write workouts or other healthy actions in your planner and treat them like appointments.
5. Find solutions for your usual excuses.
Write down your most common reasons for not doing something healthy, and brainstorm strategies to deal with them.
6. Do it daily.
The more something is part of your everyday life, the less you'll have to think about it.
7. Change your focus.
Look at what you've accomplished as opposed to what you still have to do. Pat yourself on the back!