Hi there.. I would say if you havent done much exercise lately, just go easy, and just do things to start with, in small ways, say, walk a little each day ( just a little to start ) but build up to abit more each day until you find you can manage abit further.. and do things like bending, stretching, slow dance to your favourite radio station a couple of minutes, just be more mobile..I once read that ANY movement is good, even for people who arent really active - they say people who are always doing housework, or even 'fidgetty' people are doing some good !
What I'm trying to say, is start to be a little more active,and as the days and weeks go by, and the weight comes off with dieting, you'll be able to do more and more, and it should get into a habit.. A little exercise of ANY kind every day is better I think than jujst an odd burst of intensive stuff once or twice a week..
and good luck.