Inappropriate Credit Card Use
Charging superfluous items to your credit cards, especially stuff you can't even afford, is the worst thing you can do. Charging your cards over your credit limit and only paying the minimum will lower your credit score as well as put you in a deep hole of debt. Limit yourself.
Only use credit cards for emergencies. Or use them to take advantage of rewards if you pay the balance in full. Paying the balance in full is the key here.
You Don't Save Money From Every Paycheck
Saving money may be impossible if you're struggling to make ends meet. But if that's true for you, then this is the most critical time to save. Save one percent of what you take home and build up. How do you expect your situation to improve if you never start saving?
You Make Impulse Purchases
Think about how many times you've made a huge purchase and find yourself all out of money at the end of the month. Those impulse buys aren't truly satisfying. The initial feeling wears off quickly.
The purchase may even make you feel resentful when you realize what you've done. Always think about your purchases for a few days before deciding. Often, urges will subside.