Yeah, helmets are great, even in woodland, putting a helmet next to a bush or something can make a decoy very easily.
If you are using ghillie and a wrap on your rifle, you can get some sticks and leaves, then make a ball from sticks and leaves, and put a long stick (some leaves around it) "aiming" where enemy would come, put it in an obvious sniper position so they'll see it. They might try to flank it, giving you an opportunity to shoot them when they try to be sneaky, moving slowly and stuff.