There are tons of ways to get motivated. I use and practice a lot of them both myself as well as with my clients.
New Years Resolutions, an upcoming event/vacation, etc. can all be reasons to get in the gym and finally make your health a priority. However, although I do support any reason to start or feel motivated along your journey...in my experience, a much more reliable approach to consistently fall back on is discipline.
Both are important and have their place. However, Motivation can be fleeting.
You may feel motivated for a little while and then fall off and before you know it, you have given up on your goals completely. Instead, try using discipline and keep yourself accountable towards your own goals. Become disciplined about what you eat, your rest, and of course, your activity. Staying disciplined towards your goals and keeping yourself accountable will be the backbone to your success whether you feel motivated or not.
Again, I do use motivation and see where it is very helpful. For example, I use imagery and place different images of goals of mine everywhere. My background on my laptop for example is a Black Belt. If I'm ever feeling lazy along my martial arts journey, I open my laptop and immediately see my end goal. That's one way I use a motivation tactic to keep myself on the path.
An example of my discipline is that since I started martial arts, I decided I would never skip a week of training (except for injury/ sickness). Not one week. Never. The discipline to never miss a week forced it to become a habit in my life and I am there, much more than once a week.
My point is, motivation is an important tool but having discipline in your life will carry you to places motivation alone could not.
Find a reason or a goal. Think about it daily. Work towards it and let nothing stand in your way.