Do some scouting ahead of time. Drive there and physically watch for ducks in an area. Don’t just assume they will be there because there is water there.
The Mississippi river is a good place to duck hunt. HOWEVER, if you are new to a river system, be very, very careful venturing into the backwaters. It can be an incredibly dangerous place in a small boat loaded with hunting gear.
The lakes from Faribault west to Mankato are also some pretty good areas to focus in on. And much safer for a new hunter.