I'm a ex-West Virginian, so the tips I have are mostly from hunting in the wild wild West. We hunt Utah, Montana, Canada, South Dakota, and Idaho. I think the biggest mistake we see (or hear) when we're out hunting is bad callers. There are a few basic rules to calling:
1. Quit squealing! Lots of callers try to blow into that thing as hard as they can, have you ever heard a duck that loud? It sounds like a kazoo!
2. Know when to use each call. Don't use a feed chuckle in 12 feet of water! No ducks are feeding in that water. Ducks usually only feed in 12 inches of water or less, and they have a good idea of the water depth. Also, don't use welcome calls to ducks that are coming into you already, just quack them and they'll land! There are a million calls you can use, but knowing when to use them is key.
3. Don't blow only 1 call for each duck that comes in. Even though there is nothing more beautiful than that hen mallard call, don't try to call teal, redhead, cans, or any other ducks with it over and over. Every now and then they may land, but not consistently. Learn all of the different calls if you want to kill all the different ducks! (and if you get the wood duck call down, let me know!!) My personal favorite this season has become the Duck Commander Whistle. You can make lots of different sounds with this, that is useful for a few different ducks (pintails, teal, greenies, widgeon).