I know I am not as good at this as some but there is nothing I like better than getting things I will use for free. I have greatly increased my ability to do this by doing the following:
1) Clip coupons for all groceries I would use, even if it is not something I would buy all the time. If I would use it if the price was right (ie. free) then I will clip it. I file my coupons alphabetically and this takes less than 1 hour total a week. I do it while I am watching TV.
2) Scan the grocery store sales circular weekly and see what is on sale that I would use,and that matches coupons I have. I also keep a running list of things I need to buy and try to match coupons to that also.
3) Bring my coupons with me. I have them in a little index card file box and always take the whole box to the store. This way, I can always take advantage of a surprise sale.
4) Shop stores on double or triple coupon days if available. My regular store doubles coupons up to $.99 every day - I love it.
5) Keep my eye out for unmarked sales on items I use regularly and also try to combine with a coupon.
By using these 5 steps, I usually can net a few free items each week as a part of my regular weekly shopping trip. For example, Betty Crocker Scalloped Potatoes (yes, from scratch is better but the kids love these and I have been known to make them) on sale $1.00 each. I combined this with a coupon for $.50 off which doubled to FREE. Another example, Fleischmans Yeast 3 pack strip, on sale for $1.50. I prefer to buy jar or even from the natural foods store but combined with $.45 coupon, doubled to $.90 plus register coupon for $.50 off next grocery order brought my cost down to $.10 for the strip. Not free, but not bad at all.