I started couponing last September. My advice would be to start small and as you get more comfortable you can branch out to more stores/more coupons.
We started just with the Sunday insert coupons and bought one newspaper a week. For the first couple of weeks we just used coupons for anything we wanted to buy even if it wasn't on sale. This wasn't the best use of our coupons but it helped me get familiar with using coupons and not feel overwhelmed by going from never using them to handing over 50 at once.
The best thing I did, a couple of weeks later, was to spend some time looking at couponing blogs and finding out which was the best for me. I settled on Living Rich With Coupons which does a good job in covering the stores in my local area (PA/NJ). They post store 'matchups' where they show which coupons match which sale items and they nicely highlight which items are at a good 'buy it now/stock up' price, which was great for me as i'm not always sure what price is a 'good' price for something. I also belong to a couple of couponing pages/groups on facebook
I largely stick to one grocery store. I have a store card and I stack store coupons to manufacturer coupons. A couple of months ago I started printing online coupons to supplement those I get from the Sunday newspaper. Again, if you find a good couponing website, they will either maintain a database of online coupons or point you in the direction of where to find them.
In the few months I've been couponing, I've amassed a little stockpile of household and beauty items - laundry detergent, shampoo and conditioner, soap, body wash, dish soap, toothpaste, feminine products etc. that I've gotten for free. Getting this stuff for free cuts my grocery bill a lot and makes me feel better about spending money on the food items that we like but rarely find coupons for.