Its sounds like the common cold.... which really isnt a sinus infection but can cause one, if you dont take care of the sinus congestion that is caused by the cold it will probably lead to you getting a Sinus Infection.
Pretty much nothing you can do about preventing getting cold besides stay away from people with it, and truthfully that isnt isnt enough most of the time. Vitaman C can help in preventing a little and maybe get rid of it faster once you get it, but I think one of the best methods is lots of rest and hot liquids.
Germs are everywhere... Nothing really you can do about them, unless you wanna become one of those germaphobic people that shut themselves away and carry a rag to open doors and dont shake hands with people. If you dont have immune disease, elderly or just coming out surgery or something, there is no real need to be afraid of common germs in my opinon.
Its summer time here in Southern United States nothing really to complain about besides Allergies from pollen. *Knocks On wood*