6. Keep AC filter clean and keep it on.
AC is one of the things which need to be cleaned often. As it brings in the air from outside, it might contain pollens or dust as well. But as the filter is there to save, it also needs some cleanliness. So try cleaning the filters of your AC and if not, replacing would be fine too.
Keeping the AC on would be preferable for people with allergy. Because closing all the windows would not let any allergens to get in. Rather than the natural wind itself AC would be a good choice.