All of the above tips are good, and Trevor's point re: combing the water top to bottom is one of THE most key tips, it the the most key of them all!
In March on Georgian Bay, the smelts really start to ball up and move. You can actually see them right under the shack some days. And the laker bite can be incredible with fish to 20 pounds.
Best tip I can give you is to move both horizontally as well as vertically. When we get the trucks on the ice, we'll often cover a lot of miles tagging 3 fish here, 1 fish there, 5 fish here etc. Biggest mistake I see guys make is hole-sitting day after day. On hot spots this can work, but moving around puts you over top of new fish that seem like they haven't eaten in months! Nothing more rewarding than rolling up on a new spot and having a big laker unload on you jig right away!
Our best baits:
-Williams Whitefish, Wobbler or Bully
-3" hammered finish Little Cleos (blue/silver is #1)
-2"-4" Swedish Pimple
-Blue Fox Tingler
-Hopkins Smoothie
-Mr. Champ/Kastmaster
-Luhr Jensen Crippled Herring
-Hair jigs with meat.
The later in the season it gets (more into March/April) the more and more chartreuse dominates as a colour. Don't ask me why! Gold, silver, copper, blue, pearl and white are all no-fail colours.