Inside the airplane you will a windshield wash liquid and disposable microfiber coath like these:

 

 

 

 

 

 

 

 

 

1. With a water bottle or hose rinse the windshield to remove big particles.
2. Spray over the windshield the wash solution and wait a few seconds.
3. With the microfiber without applying much pressure to the surface, remove the wash solution (and dirt). Use all sides of the microfiber to maximize its use.
4. Carefully repeat the process until the window is clean.

 

I recommend watching the following video for more cleaning tips: