Mount the aluminum frame of the window to the interior side of your window.
How to insulate around doors and windows.
Install window insulation panels.
Placing the insulation on the outside of the 2 bys left keeps the header warm and puts the thermal break on the outside.
Typically there is little room for insulation between the doorjamb and frame much too little room for typical fiberglass insulation.
Then fill in the gaps in insulation with foam which will seal around the window.
Simply cut the boards to size and fit them in place.
Weatherstrips are an inexpensive way to help seal drafty doors and windows.
8 diy ways to draft proof the doors windows in your home.
Another solution to dealing with a drafty air conditioner is to replace your wall or window unit with an hvac system.
Apply rigid foam insulation and foil.
Do not use one that has bleach in it.
When you purchase a window panel kit you should get all the necessary components and specific installation instructions.
Each frame has weatherstripping around the perimeter and that weatherstripping should seal the existing window.
In an entry with a glass door try hanging a floor length velvet curtain directly behind the door pulled to the side during the day it would be a dramatic decorative accent and at night when pulled shut it would provide an extra layer of warmth between the glass and the great outdoors.
Expanding foam insulation works best around doors.
Foams made of hfc or propane propellants are excellent choices.
You can buy a kit from your home improvement center to do this with or order one from the internet however make sure the foam is for around windows.