A couple of questions for you:
1. What choke is your shotgun? If it's full choke and most of your shots are under 30 yards, you need to change to a more open choke; a full choke at 30 yards doesn't give you a big margin for error.
2. I assume you're using a 12 gauge? If not, you might consider doing so. The 12 ga. load just holds more shot, and mathematically at least, you have that many more chances to connect.
3. How well does your gun fit? If you point it at a spot on the wall, and your gun catches on your clothing, or you see too much rib, or you're wrestling with the gun to get it to point where you look, you might want to consider a stock modification. In shotgunning, "the swing is the thing" and your eye is your rear sight. If your gun doesn't fit you, it's a significant handicap in wingshooting.....
4. What loads are you shooting? There are some promo steel loads out there for sale that give dismal performance; they aren't worth bringing home. For as much time, effort and MONEY as duck hunting requires, it's false economy to skimp on your shells. Get good quality steel at the least (ie, Winchester Supreme) and better yet, if the budget permits, is Bismuth or Hevi-shot. I'm betting if you use those, you'll collect more ducks---but you do have to pay your dues before the season, with hand-thrown clays or at the skeet range. You'll see the difference !!