Shooting through windows can be a challenge at times. Here are a few tips that will help you avoid reflections and get a clean image in the end.
The first tip may seem obvious, but make sure that your window is clean, at least from the inside. You may not be able to crawl outside to clean the outside of the window, but at least its a start.
Of course you do not want to use a flash. Regardless of how you position a flash you will almost always get flare or glare even from a off camera flash. Most of the light will likely be reflected back into the room and not light your subject effectively.
Try to shoot when the sun is not directly hitting the glass window. Early in the morning or later in the day are best times to shoot. This will reduce flare, and it will also reduce the chances of picking up dirt on the outside of the window.
If you turn out lights in your room, you will not catch the reflection of yourself in the window, or other parts of your room. It will also increase the saturation of the image that you are trying to shoot through the window.
Here is a very short link reviewing some of these tips: