Check for gaps around the window frame, sash, and trim
Replace worn or cracked weatherstripping
Apply caulk to small gaps and cracks around the frame
Install a window insulation film kit
Add draft stoppers or foam tape where needed
Repair or replace damaged window locks so the sash closes tightly
Use rope caulk for temporary sealing
Replace broken or missing glazing putty
Install storm windows
Upgrade to double-pane or energy-efficient windows if needed