Occasionally I go totally broke. No matter how much money I make, I tend to use just a little bit more, and enp up having no spare money to use. I know you do that as well. Here are some tips to stop doing it.
1. Keep track of your spending
Keep the receipts from everything you buy. At the end of the day make a list of everything you've bought and how much money you've spent. If you feel bad, while writing the list, the next day you are not as tempted to buy all the stupid shit you did today.
2. Be careful, when you go out
Partying is a very efficient way to lose money. Alcohol is expensive, especially in bars, paying for cover is expensive and alcohol impairs your judgment, so you end up spending even more money. So leave you credit cards at home, and only take cash and only take the amount you intend to spend.
3. Learn how to cook
Restaurants are expensive. You can eat as well, or even better, at home, if you know how to cook. You can also invite people to cook with you, and spend the time networking. That way you don't even lose time.
4. Stop treating yourself with something nice
Sometimes you feel down, or tired or something. You want to buy yourself something nice to make you feel better. I usually buy chocolate, which is relatively inexpensive, but the money adds up. The worst thing is, you don't even feel better. Instead you should go to the gym or running or meet a friend.
5. You don't need that many new clothes
Only buy new clothes, when you absolutely need them to impress somebody or if you walk around wearing rags. The same goes for jewelry, but not for toothpaste.
6. Try to travel cheap
Travelling is great, but you can spend a lot of money doing it. Try to always do stuff the cheapest way you can. Stay in a hostel instead of a hotel, use the bus instead of flying, go to the interesting places near, where you live (I live in Finland and have never been to Copenhagen, but instead to almost every country in South-East Asia), don't buy any souvenirs, take pictures and send postcards instead.
Hope this was any help to you.