My budget goes yearly, january - December, for no reason other than that's how it makes sense to me.
I plan how I'm going to spend all my incoming money, not just clothes. I think it would be hard to try to choose a number for clothing when I don't know what my numbers or priorities are for other areas of my life. The clothing number makes itself clear when I know what the trade offs are (more money for clothes equals less money for vacations, retirement, entertainment, donations, house upgrades, or whatever else I might want).
I lump all expenses for stuff I wear into one number, just like I lump all expenses for food into one number.
I revisit the number yearly, and adjust up or down according to how the number worked last year and how much wiggle room I have given what else I want to do.
I don't have caps for how much I spend on a certain item, except that I guess the budget itself becomes a cap. If you have $XXX left for the rest of the year, and you decide to spend $XXX of it on a pair of jeans, then there goes the bag or shoes you want. Suddenly, expensive jeans aren't as attractive.
Like Sterling said, budgeting takes some practice. You'll experiment and adjust to find what works. But my biggest tip is to plan your spending across the board, so that you have context for the amount you're allocating to clothes, and it's more clear what the impact of that amount is. (This also gives you freedom to spend, knowing that you're not having any negative effects on other life areas, because they're allocated for, too.)
Oh...and my other tip is this: expect resistance from yourself. When I started budgeting, I didn't like being told "no" or "wait." It was a rocky start, but worth it down the road.