Whenever you see one, clip it and store them. For better organization, keep a coupon binder. In the binder, put pouches with differing labels on them. When you find a coupon, just stick it in the appropriate pouch. When it's needed, it'll be available for your use.
Grocery lists are necessary for a smooth shopping experience.
Keep an ongoing list of things you need. This way when you run out or are running low on something, you can just write it down. When you're actually shopping, try to stick as close to your list as possible. This will help you stick to your budget as well. Buying store brands can help your budget.