There is something to be said for setting goals. Nothing lofty or vague, but real concrete goals that you commit to. Having goals that are tangible make working out so much easier.
For example: I always wanted to run. By committing myself to a 5k or two (or ten!) which have to be paid for in order to participate... I am committing to something. There is something on the horizon that I have to train for, work towards, and be present for.
In all the years I have struggled with losing weight, there has always been the goal of "I want to lose weight". But that is so.... foggy. There is nothing to really measure against there. How will you know when you reach that goal? If you lose 5 pounds? 10? 50?
However, if you change it to "I want to lose 10 pounds", there is something significantly measurable there. You have something solid to move towards with your fitness routines. While it may take you just as long to lose those 10 pounds even with setting a goal, you can gauge your success far easier. You aren't forever on the train of "Not there yet." If you don't define what "there" is.... how will you ever reach your destination?
Right now I'm working towards NOT getting leg cramps while running and getting my per mile time down to under 16 minutes while running a 5k. Two very measurable things. It helps with motivation. If I choose to NOT get up and work out, these goals get further and further out of reach.
When you're setting goals, though, remember to set something that is achievable. Saying, "I want to be a size 2 by this time next year" is probably not something that will happen. I am a size 16 now, and I have 160 pounds of muscle mass already. I am 5'9", so being 160 pounds at my height will probably not result in a size 2. Something more feasible would be "I want to be a size 12 by this time next year". That is far more doable and healthy for my body.
And when you set goals, make yourself accountable. Write them down. Post them where you will see them all the time, like on your fridge, or the inside of your front door... maybe on your bathroom mirror. And tell people! When your friends, family, and coworkers know what you are trying to work towards, they can help keep you honest. They can encourage you and celebrate with you when you reach the goals you set for yourself.