For me the winter time has always been the hardest time for catching Bluegill and sunfish in general. I fish 90 percent of the time from the bank. During the winter I search for the deepest parts of creeks, ponds, and small hill country rivers. I also look for weed and grass beds. Sunfish are not that active during the winter months where I fish. I also take advantage of the warm spells during the winter when the temperature highs get into the 70's. On some winter days usually during a warm spell I get lucky and find some active sunfish in the deeper pockets of water where I fish. The bite is usually slow but have caught some very nice fish. I also use the winter time to explore other water bodies and look for new spots to fish. You never have to many places to fish.
Side Note: The times I have fished from a boat or off of docks during the winter I catch the sunnies in 15 to 20 feet of water by drop offs and brush piles.