I hate using decoys early in the season. Turkeys can pinpoint your calling to within a few yards, and early in the season if they're interested --- they will search for that hen.
Later in the season, I like to use a pair of hens. I use an older collapsible foam decoy (I think it's a delta), which I set directly on the ground. I then add a bobble head to mimic a feeding hen, and set her about 5 yards from the other deke.
I place the dekes facing directly at me, about 15 paces from my position. I typically will place them either directly in front of me, or slightly to my right. I anticipate the gobbler coming from my left, which gives me plenty of time to zero in on his snowball...
I have stopped using dekes in the woods, and will only use them on pasture edges. In my opinion, well at least in NY and New England, the birds typically don't stop too often in the woods and therefore the hen dekes are just too unnatural. Most of the turkeys feeding/dusting areas and "lazy time" is spent on pasture edges, and I believe that's why the dekes actually work better on the field edge.
Two things I consider paramount to successfully using dekes:
1) Pattern the gobbler. Have an idea of which direction he comes from, and his general disposition. If he's got a harem of hens with him, a whole flock of hen dekes are going to be useless. You will need a jake or a tom deke to entice either him or his lead hen in your direction...
2) Very little calling ,and then very soft. Call only when he's within eyesight, or when you think he should be close (based on your patterning). In my experience, I've found that using dekes coupled with soft clucks/purrs will help you harvest that 3-4 year old nervous tom late in the season, when everyone else is either tagged out or watching the Indy 500
If you're after a 2yr old, leave the dekes at home and just keep switching calls/cadence until you get a bird excited. He WILL find you...
S&R