This is my third month setting a budget. It is hard to start and is a "work in progress" right now. What I did when I set my first budget was to look at what I spent in my previous month and vowed to get it down to something "reasonable".
My first month was May and I set it at $500. We spent $738 (ugh). I said I would try to get that down to $500 in June. We did well most of the month and then did a Costco run on payday during the last week. That ran us over again ($625). But, I had to look at it that we did spend over $100 less than the previous month, plus we also did some "stocking up" and that sets the amount higher.
I'm setting our goal again at $500 (we're a family of 6) and trying harder to get it down. Since I have now taken 2 months to get more of a shopping strategy, I think it will go better (at least I'm hoping so).
I think you do need to plan for those stock up months. Don't beat yourself up if you go over your goal. You did really well with the coupons!

I had to figure my shopping pitfalls and it took a couple of months to do that.
In my situation, I found that making multiple trips to the grocers for the coupon "deals" caused me to spend more. I got some great deals, but also bought other stuff that we really didn't need to spend the $$ on. We went back to the payday Costco shopping runs instead and it does seem to make a difference for our family.
So, I suggest looking at your check register, etc. and see what you did spend during the month of June and/or May. If that sounds reasonable, then stick with that amount. Make note of if you did alot of stocking up last month and set your July budget according to whether you plan on doing stock shopping or just filling in stuff (milk, veggies, fruits, breads, etc...).
HTH and good luck!!!