Believe it or not, I didn't mean for that ^^^ to sound like a joke -_-
I'm tired of trying to motivate myself.
You don't have to motivate yourself.
You just come up with a plan based on what you are trying to accomplish and slowly work at your plan.
After a few weeks it becomes habit. You'll find that days when you have to skip your workout, for whatever reason, that you wish you could have done it.
But be careful skipping workouts. That becomes habit as well...
There are several fitness plans that you could adopt based on your goals. If you are going for strength there is 5x5 and Starting Strength.
If you are going for bodybuilding those probably apply too, if you are just beginning.
If you are going for cardio there is a couch to 5k running plan that I got off the internet. It worked really well. Then 5k to 10k plan. I got an app called MapMyRun to figure out how far 5k was and it was off to the "races"...
I've modified every plan I've followed depending on how well, or how not so well, I was doing.
We're at the age now where, if there are people that depend on us, we have to take care of ourselves. So if you don't do it for you, if you are not your own motivation, just think of the people who depend on you.