simple
An issue of Men's Health magazine had an interview with Matthew McConaughey , and he was talking about his exercise workout, that involved a lot of running. He said his best advice was simply "put your shoes on". If you're going in the morning, roll out of bed into your shoes. If you're going later on, do whatever you have to to automatically get your shoes on. If shoes don't make sense, use whatever else works for you, but the point is to get that first step to happen automatically.
No one gets to the gym, or puts on their workout clothes (if at home), or puts on their running shoes and THEN decides not to workout. The first step is the hardest, so listen to our friend Matthew and just "Put your shoes on".
Personally, I think motivation is about leverage. You need a reason - one that will override the reasons not to. Imagine what will happen if you DO go workout and also what will happen if you DON'T. Which version of yourself do you like better?