There may be a handle that lets you open the window, have you tried that? :)

Other than removing the problem that way, what you are doing is pretty much the best option. By putting the lens close to the window, you are getting any dirt on the window out of focus. Every part of the image usually passes through every part of the front lens, which means that out-of-focus dirt has to be pretty severe to affect the image at all.

There are third-party lens hoods made of rubber; those might work well to make a seal that keeps light from getting in between the window and the lens.

Try to take pictures at a straight angle through the window if possible. If you take an image at a too great angle, you will get light that bounces inside the window glass, causing a displaced ghost image. With double- or triple-glass windows, this effect will be more noticeable.

A polarising filter can be used to reduce some of the reflections in a window, but it does also affect any light from the outside that is reflected somewhere. So sometimes, you will not be able to keep the reflected light that you want from the subject while blocking out reflected light from the window.