I have had a budget for about 20 years, and when I took a break for a few years, I gradually started spending too much, and realized that I felt guilty no matter how much or how little I bought! When I started budgeting again, I saw the benefit of keeping track of what I was buying, which made me feel much more in control.
Use a Spreadsheet
My husband and I started a household budget when we were first married, and we used Microsoft Excel, but there are other spreadsheet and budgeting products. Even paper and pen will work, just use what you like.
I save receipts for everything that I am budgeting for--clothing, shoes, jewelry and accessories. I don't include beauty products or appointments, because they aren't as difficult for me to control. Create categories as you see fit. Keep receipts from these categories in your wallet, or designate a basket or bowl in a prominent place at home, which works well if you are budgeting as a couple for your household. This helps to have them handy for returns as well. If you do return something, make sure you credit your spreadsheet.
Record Purchases Once a Week
Choose a time, for example, Sunday evenings, and sit down, gather your receipts, and record the purchases onto your spreadsheet. This will give you your current balance. If you do this, you will always have a number in your head that's available to spend.
Set a Monthly Budget Amount
This is the hard part, and it's different for everyone. Obviously, you need to be able to afford it, but beyond that, try to come up with what you would like to be spending. You can make it quarterly or weekly amounts if you'd like, but monthly seems the right timing for me.
Keeping my clothing purchases within a budget has helped me to shop more intelligently. I shop at a variety of stores, such as Target, Nordstrom Rack, and consignment, as well as traditional clothing stores. Budgeting also helps me make better use of the clothes I have in my closet, by wearing them more often, but mixing them in different ways. I am more careful with what I buy, making sure it is the right fit and color, and that I really love it. It has helped me to be aware of major store's sales and keeping some money available for those sales.
Using a budget allows you to save up for large purchases you otherwise would think are too expensive or you would feel guilty about. As you purchase items, be very sure you want to keep them and wear them. This can take some time and trial and error, so always save receipts and invest the time to return items that you decide you don't like. Also, if something is in good condition, and can't be returned, sell it at a consignment shop and use that money for new clothes.