I find it helpful to use cash, and have no spend days, set a budget. Examples:
1. This year I am pledging to buy no new clothing.
2. I have set a grocery budget of $80/week.
3. I am trying to reduce eating out, so we had a 6-week stretch of zero eating out (sometimes it's easier to have a budget, sometimes it's easier to have the budget be zero).
4. Aim for a certain number of "no spend days".
5. Limit what you spend money ON. For example - I make trips to the drug store for needed things like medication, sunscreen, etc., but have to say NO to everything else.
Beyond that it gets tricky. I could not "waste" money by looking for deals on used clothing, etc., for my kids and such. Or by shopping sales for sunscreen, etc., but it gets super tiring to find the best deal on every little thing. I find it easier to just NOT buy things I don't need, and not worry about paying $2 for a tube of toothpaste instead of $1.