I've learned for myself, I have to take baby steps. I used to try and be gung ho and say, "okay, I'm going to work out 3 times a week." While it would last for a little while, I wasn't consistent, and eventually I'd stop altogether.
What has really helped me is a pedometer. I found that while I don't mind going to the gym, I don't motivate myself to go unless I have to meet a friend or something. With the pedometer, in the beginning, I'd get an idea of how many steps I walk during the day. If I do nothing but go to work, eat lunch in, and go home, it's about 3000 steps. The goal was to get more steps, and I'd do it gradually. Walk to the farther bathroom. Catch the elevator 3 flights and walk the 4th, etc. Dont' worry about getting the closest parking stall. It may not seem like a lot but ANY kind of movement helps! It doesn't have to be about jumping on a machine, lifting weights, or the aerobics class. The goal is to get up to 10,000 steps a day, and while it seemed unlikely in the beginning, most days I get at least 8,000 steps!
BF and I also found a walking buddy. We have a standing arrangement to walk every Monday and Wednesday after work. If one of us can't make those days, we try to reschedule for Tuesday or Thursday. What keeps us accountable is that she doesn't drive, so we have to pick her up.
I also learned that there are a lot of commercials when watching tv! I figure, if a show is scheduled for an hour, there are about 20 minutes worth of commercials. You could get a lot done in 20 minutes! Get a pair of light dumbells (2 lbs, etc.), and just lift those during the commercial -- heck, you can even lift them while you're watching tv! I also have those stretchy band things. Sometimes I just stretch my muscles out. If you're really ambitious, you could do some crunches during the commercials.
You get the idea...just take it slowly and keep in mind that ANY MOVEMENT HELPS. Fit in small things in those little pockets of time you have.
You can do it!!!