There are 3 things that matter:
1) Learn to call. Really learn. Not $20.00 Wal-Mart calling like you hear so often. Get a good CD because if you can't hear good calling you won't become a good caller.
2) Learn to work ducks. You have to be able to do #1 to do this. Go somewhere big and open like a giant public marsh and call. Watch how ducks respond. Learn when to use what, and when to shut up. This, to me, is the essence of duck hunting. Pass shooting ducks is no different that dove hunting or blocking pheasants, or shooting clays. It's purely shooting. But duck HUNTING is about making the ducks do what you want, and it's a beautiful thing.
3) Learn to shoot. Really learn. My soul dies a little every time I sit in a public marsh and watching the idiots with the 3 1/2" Mossbergs banging through boxes of shells on ducks at 80 yards. They can't do 1 or 2, so they make up for it by shooting roman candles. Instead, take the time to shoot some sporting clays or skeet. Dove hunting is even better. NOT TRAP. You need a variety of presentations and cases of spent shells behind you. A piece in SCI a while back suggested something in the range of 2000-2500 rounds before the average shooter could close in on being a good shot. I've never counted, but I know it takes a LOT of shooting.
Obviously it's easier to learn from someone but be careful who you pick. Lots of guys will tell you they know #1 #2 and/or #3 but they don't.
The other things come naturally. Gear isn't that important beyond a shotgun and a call. Finding places, scouting, blinds, boats, duck ID, dogs... those things all come naturally when you've got 1-3 mastered.