There is a lot of good advice on here, a lot of different opinions which is important as everyone is different. I started exercising a good few years ago as I was unfit and unhappy so I thought I should do something about it. Getting started was really hard, I'd look outside, see the weather and think of a reason not to go, problem was I then felt worse about doing nothing. I started to concentrate on what it was about exercise that I liked, it certainly wasn't getting out the door in bad weather, nor was it the first 10 mins when everything hurt. I enjoyed the feeling of finishing my run and the warm shower after it, I enjoyed getting back home and feeling smug about the fact that I was doing more that most about doing something positive. I still go through this every year when I start out after the winter, I started again this week. I hate trying to get fit after a winter lay off, I try to exercise during the winter but I don't cycle in high winds and we've had a lot of that this year so I'm very unfit at the moment. Its is important to find a form of exercise you enjoy but we all go through times when we are low on motivation and cant be bothered, it is also important to find something within yourself that pushes you when you cant be bothered. For me it is the look on peoples faces when I run or cycle past them, I know I'm doing something they wish they could do. I have a story about running on the West Highland Way and passing a group of 4 girls with 4 blokes. I passed them on the way back to the car later that day and the 4 girls were so impressed with my efforts they wouldn't leave me alone, the blokes were not so impressed. The feeling I got that day has kept me going for years.
Good luck with whatever you do, but do something that makes you feel good about yourself.