This is a great habit to keep not just the first few months of 2020, but the entire year. But it’s not easy. In the first month, you may want to physically write down each purchase you make in a notebook that you carry with you. Sometimes physically writing it out makes you more aware of what you’re spending.
As time goes on, you may consider moving to a smartphone app to track your spending. Many budgeting apps allow you to enter each transaction as you make it. You can record it in both the account and the category so you can stick to your budget and recognize your budgeting weaknesses.