One of the best ways to make sure something gets done is to be prepared! So if you want to improve your diet, or improve your exercise or whatever, you are more likely to succeed if you plan ahead.
So here is a simple calendar for the coming month. Print it out and stick it up on your fridge or bathroom mirror or wherever. Use it to decide in advance what change in your diet or exercise behaviour you want to make this month. Then simply tick the boxes each day you succeed.