Keep receipts, and know your money. You should be able to tell somebody how much cash is in your checking account. As others have said, keep a strict budget. Maybe write out a budget at the beginning of every week or every two weeks (however you get paid), and account for all of your habits, be them soda, coffee, cigarettes, or speed.
Cut down on those habits.
And Kahl is right, don't eat out. That is a killer. If you have even a little bit of time to cook something big and live off of it for a few days, you should always do that. I need to start following this rule.
Hybrid Mode
