This tip is not so much on how to wake yourself up early but on how to fall asleep faster. Don’t eat too much right before bedtime – it’s that simple. You may have a light snack 2 hours before sleep time, but not later.
This advice has a simple explanation. Your organism stays awake digesting the food, so even if you fall asleep a part of your body is not “sleeping”, and overall you have less effective sleep which is not restful. You will need more sleep. which in turn will prevent you from waking up early easily. Same applies to drinking lots of water, soda, or any other beverages – you will feel discomfort and will have to get up to go to the bathroom during the night. If you feel thirsty, put a glass of water near the bed and take a little sip from it from time to time before you fall asleep or when you wake up during the night.
Please note that going to bed hungry or thirsty is not good either, and can be just as disruptive to sleep as going to bed too full. Having a light snack or a glass of milk will help you ease the hunger. Check this EatingWell article to decide what to eat for a good sleep: