Couponing

For a while now I have been interested in couponing. I will go to all the websites, and get the Sunday paper, but it does not seem to be working for me. Several of my friends report on how they go into the grocery store and get $200 worth of groceries for like $30. I can't do that! One time I did get about $30 off my bill, but I can't seem to get the hang of this. I must be doing something wrong. I know you are suppose to wait for the sales, and use 2 coupons if you can, things like that. I guess my problem is, when  I go to the grocery store I need what is on my list right now, and I am on a tight budget, so I can't afford to get those extras just because I have a coupon. I have no idea, what I am doing wrong. If anyone has any ideas I will take them......