A few practical methods can help:

• Press the lens close to the glass: A flexible rubber lens hood works especially well. If you place it flush against the window, it blocks stray light from behind and around you, which can greatly reduce reflections.
• Use a circular polarizing filter (CPL): A good CPL can cut many reflections from glass, especially when you adjust your shooting angle. Its effectiveness depends on the angle and lighting.
• Change your angle: Reflections are angle-dependent. If possible, move so bright objects behind you are no longer reflecting into the lens.
• Choose softer light: Early or late in the day can help, especially if direct sunlight is not striking the glass or subject.
• Watch the light sources: Reflections come from light hitting the glass at certain angles. If strong light sources behind or beside you are outside those angles, reflections will be minimized.

In practice, the best results often come from combining methods: use a rubber hood against the glass, add a CPL, and adjust your position slightly.