I hunt quite a few cattails but have generally found that the huge parcels that are a "never ending sea of cattails" generally don't produce the greatest. There is just too much cover for the birds, they really don't have to get up unless you dang near step on one. When you do shoot one, retrieving one seems to be difficult, even with the best of dogs. They are tough to walk, nothing worse then getting a half mile in on cattails then still having to get a half mile back out.
Smaller, narrower cattail strips, or football field size areas within some other cover, they seem to produce very well and are usually what I search for. As far as tactics, hunt slow, stop often. Your footing isn't always the greatest - quickly push through the areas that don't present a great shot, slow down in the areas that do produce a quality shot opportunity. Use the wind. Push the birds to areas you still have access to if possible. Lots of them get up at the very end when they are finally out of cover.
In south central MN, they are still not froze over the greatest. I went through a few spots last week that ranged from knee to hip high. Unfortunately I just kept thinking "a little further in will produce a bird" but all it did was produce more wet boots and clothes... Hopefully after this mid-week cold snap all cattails will be good the remainder of the year.