I have found being obsessive about planning makles it easier to get back into the swing of exercising. For me, like many people I think, commitment to a regular exercise program requires planning to fit it into your busy day. But getting to the point where it is a routine can take a large amount of will-power in the beginning.
Schedule your workout time just like any other very important activity. Write it on your calandar in PEN. Give it the importance of a doctor's appointment. You cannot miss it. If something comes up, think long and hard if accepting the other thing if that means skipping your workout. And do not be afraid to be selfish with your time. For example, sometimes I workout during my lunch hour. If a meeting comes up during that time I simply say I am unavailable at that time and suggest another time. It is none of their business what you already had planned. All they need to know is that they are busy.
I also suggest planning your workout time for the entire week in advance. This way as things come up through out the week you already have your workout time scheduled in and can plan around it.
Good luck. Since you used to be an avid exerciser, it will be easy to keep going once you get back into the routine. But getting back into the routine will take some effort.