What's Your Budget?
Knowing how much money you have available to you for the entire month, before you start spending for that month, is crucial. Figure out your total income for the month, and then subtract all the monthly bills you need to pay. This includes expenses like rent, utilities, loans, credit card, internet, and phone. The remainder is your budget for the month. This is the total from which all your extra expenses, like food, transportation, and entertainment, will subtract. Stick to it.
Needs Versus Wants
Make two lists. One list with all your needs and another with all your wants. The needs should be things that you cannot live without. This will include things like deodorant, shampoo, and food. This does not include things that you really, really want. The wants list will be anything, and everything, that you want. This list can be separated by things you really want as opposed to things you would like to have but aren't as important to you at this very moment.
Save your money. Set aside a percentage of your income each month. This doesn't have to be a high percentage. Five or ten percent should be manageable. Open a savings account, and put that money in it. This will be useful, whether for an unexpected expense that crops up, a rainy day, or maybe for that vacation you've always wanted to go on but never had the money for. Now you can finally have that money, by saving little-by-little each month.