For the next few months, you'll want to start getting your pantry together. The reason I say for the next months, and not in the next grocery trip, is because you're trying to save yourself money. When you see a good price on something, you'll want to buy it in bulk. Don't buy it to last you one week, buy as much as you'll need until a good (or even better) price comes up on it. So if chicken breasts are on sale for $1.68, which is a great price, buy a bunch to last you until it becomes that price again (and as you do this more and more, you'll see a trend).
I only have a small freezer, we live in an apt, so we don't have space for extra freezers. So, I have to be careful of how much I buy to freeze. I usually buy 8 3-packs of chicken when they are at that price. Then I don't buy chicken again until it goes to that price again. Just plan your meals around the food that you have, and you'll save big money. Right now, I don't have ground beef in my freezer, which is driving me crazy - i will only buy it at $0.99/lb, and either I missed it, or I bought way too little!
Another thing on that point, I try not to buy things that are going to take up space in my freezer: frozen dinners, boxed things, a large amount of ice-cream, etc. I either take them out of the box or try and finish it quickly. Plus, most of that stuff is more expensive than making a dinner from scratch, and definitely less nutritious.
For a little while, when you're beefing up your pantry, your "need" list will be long when you go to the grocery store. But as you get your stockpile up, your "need" list will grow shorter and you'll be able to spend less every week. Every time you make dinner and you see your stockpile getting short, make a note so that you'll be on the lookout for the sale price of the items on which you're short.