Now i am going to the gym 6 days a week and it is very fun.
what i did was similar to Alex's:
I wrote my general goals everyday and one of them being healthy and fit. I imagined myself that way whenever i can. (Still doing these things)
My first goal was to make it a habit and a fun one. My first rule was to go the gym. You dont have to exercise, just wake up in the morning and 'same time everyday' go to the gym, listen to your ipod or read something. Do not force yourself. Run if you want but be there every morning at the same time. You will end up doing light exercises and then progress from there.
In 2 weeks i lost 4 kg fat then began gaining muscle and in a month i quit smoking.
In short:
1- Write your goals
2- Visualise yourself as your ideal self
3- Make it a fun habit before doing the actual thing
4- Measure your weight, size etc... Watch your progress
5- Begin with little steps not pushing yourself.
6- Celebrate and be grateful for your every success.
7- English is not my native language sorry if you dont understand
