There are a variety of ways to get coupons:
My personal favorite is my subscription to the local newspaper. Some newspapers offer deals to couponers. My local paper does.
I get 5 Sunday papers as well as a daily paper for around $20 per month, which is a lot cheaper than buying them from the newspaper dispenser. So each week I get 5x each coupon insert. I live in the northwest and also get Albertson's Double coupons some weeks (more info later in the post).
There are also websites that allow you to print coupons. My favorite is coupons.com. You can print each coupon twice per computer. So if you have 2 computers you can print 4 coupons.
Another way to obtain more coupons is a clipping service. That means someone else cuts out the coupons for you to buy on ebay or other website. This comes in handy when you want to buy a large quantity of items (like they do on Extreme Couponing). I personally haven't tried this before, but have heard that if you do this it is a good idea to call the store manager to make a special order so they have enough of the product for you.
Albertsons puts "double coupons" in the newspaper also. These are my absolute favorite! That means I can double a $1 or less coupon, taking up to $2 off of an item. Most of my sweet deals (freebies) come this way! (I live in the northwest, and I'm not sure where else these are offered.)