Mix equal parts of white vinegar and water in a spray bottle. If you're low on vinegar, mix a solution that is 1 part vinegar and 2 parts water. Alternatively, use rubbing alcohol instead of vinegar.
Spray the vinegar or alcohol solution liberally on the ice that is frozen to the window. Wait three to five minutes for the ice to melt.
Reapply the vinegar or alcohol mixture if the ice was thick and one round of spray was insufficient to melt it all.
Prevent ice from freezing on your windshield overnight by spraying the same mixture on the windows before you go to bed.