I need to insulate my patio doors but I am not sure what to use or how to go about it. They are sliding glass doors and they let in a lot of air in the winter. I would like to find a way to stop the air from coming in and going out to improve my electric bill

best way is a nice new door with triple-insulated glass. double-pane has done well for us.

if you have a multipane door but the seal is blown, so it looks like clouds in the glass, local glass companies can replace just the glass in most windows and doors for a fraction of the cost of a new complete unit. call around, get estimates.

quick and cheap is to get a patio door insulating kit, using double-stick tape to cover the whole door and frame, sticking on their special shrinking plastic, and then shrinking it tight with a hair dryer. that works well, but you lose the use of the door during the winter season the kit is on.

there is no way to have your cake and eat it too... a creepy door that leaks all over would not benefit from duct-taping fiberglass batts over the windows, because most of the cold air comes in the seams on an older, worn door. new weatherstripping can help a little, but a loose worn door is not going to be useable AND weathersealed.