1. Have a shopping list because you can't do comparative shopping without a list.
2. Check the newspaper advertisements (specials) for the prices of items that you want to buy.
3. Check your list and see what shop is selling what items at a reduced price than other shops.
4. Take note of other products which are on your shopping list but are not advertised.
5. Also check the price of other items which are not on your list when out shopping and note down the price as you may have to buy that particular product later.