I always find windows very interesting when I'm taking street photographs. It adds a different dimension and a different sense of space to the images. When you shoot through the window, you catch a glimpse of what's on the other side. Sometimes reflection is inevitable, but other times it can work in your favour as it brings the inside and outside worlds together visually, kind of like a double exposure.
If you want to minimize the reflection and highlight the people, you should try to shoot at an angle and use single point focus. The next few pictures were taken using this method.
Generally speaking, I do not look for eye contact when shooting through the window, I try not to offend or embarrass anyone. My intention is to capture the moment instead of ruining it for the people in my photographs. However, sometimes I do get spotted despite being discreet, and when that happens, a little hand gesture or a smile will go a long way, and when you do get that eye contact, it makes the photo that much more striking. That is why shooting through windows is a good way for beginners to get into street photography. You can take candid photographs without being confrontational, and even when people do give you a mean look through the glass, you can simply just walk away.
If you want to get a little more creative and play with reflections, then try zone focusing when you shoot through the window. In my experience, reflections are more prominent in images captured using this technique. The next few images are examples of zone focusing and shooting from the hip.
Shooting through windows can be fun as long as you do it discreetly and respectfully. The gear you choose does matter in this regard, having a compact camera like the Fujifilm X100 series or the X70 is preferable to a bulky DSLR that draws unwanted attention.
I hope you find these tips helpful. Thanks for stopping by and have fun photographing in the streets!