store brand have about the same ingredients in them and taste the same (or look and feel the same if you are talking about clothes or other products).
shop around to many different places. in the past, we have gone to 4 or 5 different stores and looked at the prices of various items. we made a chart and then recorded the different prices of each of the items on the chart. while one store may be cheaper for a can of mushroom soup, their peanut butter may be a lot more expensive.
watch what you are buying and ask yourself if you really need it or can get it somewhere else 