Imagine yourself as the happy person you want to be. Think of situations that make you happy and visualize yourself in those situations and let the happiness flow through yourself. This comes at much later stage, when you have finally healed yourself and don't blame either yourself or the other person for the breakup. You will be ready to move on when you can remember the good times you had in the relationship without feeling the intense pain at not being together. Ask lots of them.
Information is the 'cure' for ignorance.
Make yourself conscious of what you're supplying for 'fuel'. Watch your body change and be aware of those changes. Some can be subtle, while others for a month or two, can make you want to change your appearance. If you follow sensible eating and an exercise routine, there should be no need for 'dieting'. They can be one of the most trusted sources of reliable information and solutions.