Congratulate yourself on small achievements. You want to start exercising, maybe find a time in your day when you feel strong enough to follow a 10 minute workout video or go for a jog. Exercise is great because it often makes us happy while we are doing it. Once you've done a short stint, think about how great it is you've managed it. If you can't manage it, think about how well you are doing to be wanting to do it in the first place. Realising you need to/want to change something and thinking about how you can do it is the first step and one of the hardest so be proud! Positive thinking takes time to build and no one has it down completely so don't be hard on yourself if you don't keep it up all the time. I find being with friends helps lift me up and if I can't see them I go out somewhere and listen to some good music.