There are several things you can do in order to minimise reflections:
- Shoot as close to the glass as possible, but don't touch the glass, the vibrations will cause you to have a shaky photo.
- Prevent any light from the plane from reflecting into the camera. You should turn off the overhead light for example. During take-off or landing usually the lights in the plane will be shut so it is the best moment to shoot. Some flight attendants may tell you to store away any electronics, but theoretically there are no safety concerns using a camera unless you have it connected to your phone or something.
- Use a lens hood to have less reflection, or use something even bigger than a lens hood(a t-shirt around the lens) so as to minimise reflections.
- Shoot early in the flight, while the windows are not covered in ice or droplets.