Get on the conservation atlas on http://mdc.mo.gov
and start researching some spots like swamp said. Talk to the agents for the counties you want to go. The numbers for the agents can be found on the above site also. Talk to the Biologists at the areas. Then go out and scout the areas.
Since you are new, you might not know exactly what to look for when scouting. Research the different types of foods that the ducks like to eat, time of year they like it (warm weather v.s. Cold weather.... Moist Soil v.s. Agri crops). I suggest you get to know some of the guys on here. Try to join up with them. Take them scouting with you. Buy them a case of beer, etc...... I have met several friends on here and been to spots I have never been before with them. Lots of knowledge to be gained from folks on here. Most will not post it up for everyone to see, but many of them are willing to help a guy out as long as he doesn't turn around and give that info up to everyone else.
Best way to learn is through trial and error and joining up with a more experienced hunter(s). Send a PM to some guys on here, and they may help point you in the right direction.