One good thing to do is start reading the ingredients of the stuff you buy.
If you don't know what half of it is then it is obviously chemical shite.
Also look at the % of fat, sugar etc. Visualise what you are actually putting in your body and think about what your body has to do to process this stuff (that has NO benefit at all to you) and to get rid of it.
If something is 30% fat (like some chocolate) then you are effectively eating a flavoured slab of lard, with loads of sugar to hide the taste.
Chew your food lots, think what you are eating and try to appreciate the food and taste instead of being distracted and just scoffing without thinking about it.
Try to eat when hungry, not when you are bored.
All these things got me from 13stone 10lbs to 10stone 10lbs and the opposite, after 2 1/2 years put me back to 14 stone (although to be fair, the brain aches and procedures do have a role to play in my defence!)