When the water is cold they are less willing to move , you need to take the fly to them and fish it very slow . Hi D line , short leader ( 2 feet or so ) and a floating fly . If the bottom of the place you are fishing will not allow that ( rocky and will wreck your line )then use a line and a fly that will let your fly bounce the bottom or fish just above it .
Find the bait fish you find the Pike , simple as that . Deep water is warmer then the upper layers in the winter time ( colder in the summer ) This is where your bait fish will be , be it coarse fish or Trout .
If you don't know the lay out of the lake then if poss get in a boat with a fish finder and map it , find drop offs , holes and under water structure in deeper water like reefs and sunken islands .
All that said don't rule out the shallower water on the nice sunny winters days we do sometimes get , most of all mid afternoon
Hope that is of some use to you ........