Do not keep the bird feeders at the windows or closer to windows. The birds are mostly likely to hit the windows if they come to take the food from feeder that is too closer to the windows.
Installation of patterns on the windows can help prevent birds from smashing into them. The option is not very expensive while its benefit is greater. The need for installation of patterns becomes even more important if you live in areas near the sea and other areas where birds live and roam in greater number.
You can also place vertical tape strips at a distance of about four or more inches. They should work as effectively in guiding the birds away from windows as other similar solutions. Also, this is probably the cheapest option that you can try and help save lives of many birds.
Installation of blinds on windows can also help protect lives of birds. You should keep the blinds pulled in front of windows when they are closed, so that the window glass does not offer a reflection to the birds and they avoid flying into the glass.
To obscure the reflection windows glass, you can apply any paint as a solution. If the windows glass is obscure, this should prevent the birds from flying into the glass. Do not leave windows with glass giving clear reflection of anything that sees into it.
Windows gel clings, whether home-made or bought from the market, can work as solution also. While placing the clings, give at least four inch distance for each cling. Also use a colour that is more visible to birds. This solution is similar to the tape solution and can work as effectively as the tape does.
You can also try solution of the windows film. However, choose the colour that is clearly visible to the birds and they can avoid flying straight into the glass. The solution is similar to the soapy foam and works effectively well.
You can use any shadow or shades that can keep the birds away from window panes. Do not leave window without a solution to the issue, as if you see a bird or two killed after smashing into the windows, you might feel guilty as if you have killed the birds on purpose. Every year millions and according to some estimates billions of birds fall victim to the windows crash.