I would recommend two books to you, Skip Morris' Tying Foam Flies (Amato Publisher, 1994) and Harrison R. Steeves, Tying Flies with Foam, Fur and Feathers (Stackpole, 2003) if you really want to get into foam flies. When I first began to use foam I was focused on tying dry flies for trout and steelhead in moving water--skaters, wakers and terrestrials. I have to admit that at first I was somewhat disbelieving that a Chernobyl Ant, for instance, would consistently take fish on a lake where the fish could inspect the offering at their leisure.
However, once that I began experimenting I found much to my surprise than even on otherwise technical waters, trout would go after foam flies (even Chernobyls!). Many of the standard deer hair patterns--crickets, beetles, ants, grasshoppers are more durably and effectively tied using foam in addition to or as a replacement for buoyant natural material like deer hair.
Foam can be used on sunk patterns as well. Just as clipped deer hair is used to make buoyant patterns to fish on a sunk line, like some of the dragon fly nymph patterns for example, foam can do likewise.
My favorite foam pattern for trout is a black or brown foam beetle with bright indicator (foam) tied on top. A very simple four step pattern, foam underbody wrapped slightly beyond hook point, overwrap of twisted peacock herl to front end of abdomen, tie off but do not cut yet; bring foam forward over the back tightly tie off but do not cut, tied in two sets of rubber legs of appropriate color, tie in indicator foam piece on top, continue herl body to just behind eye tie off and cut; bring foam back forward tightly, tie off and secure with with a whip finish;, now grab the end of the foam and pull enough to stretch it out a little and cut it off so that it snaps back to form a sort of blunt head. It probably takes longer to describe how to tie than to actually do it.
i agree with everything wake said. i like the club sandwich, which sometimes outfishes the chernobyl ant. glue the three pices of foam together first and then cut out your shapes. you dont need the cutters that are sold as i dont think it makes any diff. at all, it makes the fly look better to the angler. i also like ants tied with foam.