On the days you’re busy or just not motivated, how do you psych yourself up to exercise?

Usually I have the same problem, I'd never followed an exercise routine before, I have always been an slim person, without getting to a skinny point, but no strength. Starting to follow a routine has been really difficult. In those days were I have no motivation to do exercise, I think in the progress I have made since I stared and to imagine that, if I am in these point now, how my physical condition will be on a future? And I talk to myself and tell me, that future will not come, unless you continue in these road. Usually it helps but it isn't any magic recipe to be motivated, try to do it and hope you fínd everyday that inspiration to continue.
Ezra.