When planning a budget, the most important things should always come first: Shelter, food, and other basic necessities. Number one on my budget is rent. I live by the rule that housing should never be more than 30% of your total income. This number varies according to different people, but depending on your income, situation, and family size it will definitely change. Next, I cover my groceries. I like to cook, but I'm only cooking for one person, so I tend to eat less. This helps greatly, because it keeps me from eating out so often and from getting too much food at the grocery store. Finally, a basic wardrobe. As much as I love a little variety in my life, I will cover the basic necessities such as jeans, shoes, etc etc. if I need to purchase them within that month. Since I'm a great junk shopper, this usually doesn't run me more than $50 a month. Thus my basic budget includes: rent, groceries, and occasional clothing.
Next comes the optional or "wants". I include junk shopping, oil changes, gas, etc etc. The reason why I've included these as wants is because, it's my choice to drive to places, go junk shopping, eat out, etc etc. When I budget, I can limit my use of these services because I know how much money I have left after I've taken care of my necessities. Lately I've limited myself to $25 a week to pay for these things. Believe me, this is very possible. You learn to become creative when you have no money and no schedule. :)