A tip for really dirty interior windows, I always keep a spray bottle that has a little washing up liquid and water, normal everyday washing up liquid is a very good degreaser.
For really dirty windows I spray the glass with the solution. then using a non scratch sponge sourer I go over the window, making sure I get all edges and corners.
Then I have another spray bottle with deionized water, I spray the glass with the water to remove the solution and dry it off, then with a clean microfiber towel I spray the glass with the deionized water and buff off, This works very well for me.