Start thinking of all your favorite brands. Then go to their websites. See if they have a "join" or "register". If they do, they will often email or mail you coupons. It's a start.
Next, start clicking on those "contact us" links. Send an email telling them how much you love their products. By doing this, I have received coupons 95% of the time. I do not ask for coupons. I just tell them how much I love "x" product and they respond saying thank you and can we have your mailing address to send you coupons? Often these coupons are for "Free" products.
There are some places to register for freebies also. See links below.
VocalPoint - this is a GREAT one! I get great coupons from this. These q's are either for "free" items, or are so high that with a sale, they = free.
Homemade Simple - This is a neat site that often has good printables. They also periodically have a sign-up for a mailed booklet that has a bunch of coupons in it. Last time there was a "Free" Cascade jet dry-thing coupon in it. High value q's! Check back occasionally for that.