To maintain healthy habits you need to find a way to make them a forever choice, not just a quick fix. This means not setting unrealistic goals, but instead finding managable ways to create a new lifestyle that will last forever, and change your life.
For 2015 I started by setting the goal of 10 gym visits per month.
I use my bullet journal to record my exercise activity; basically an adult reward chart. Each line is a month; January, February, March and April, with 10 smiley faces.
Success breeds success. If you start with goals that you continually fail at, you're not particularly motivated to work harder. If you set a goal, and reach it,you're much more likely to achieve it again, or even more next time.