What's the best way to treat hay fever?

Allergy medicines. Hay fever (allergies) is usually due to pollens that are in the air. Some people are allergic to molds and other substances. One can wear a mask when working outdoors or when hiking. Avoid playing outdoors when the pollen or smog levels are high. Medicines such as Claritin otc, zyrtec otc, or prescription eye drops and nasal steroid sprays are helpful. Allergy shots are another option.
Avoidence. The best way to treat hay fever is to avoid the allergic trigger. Medicine wise, nasal sprays with antihistamine (like patatanase or astepro) or steroids (like Veramyst or nasonex) or combination of both (like dymista) work better than anything by mouth. These all require a prescription. Finally if the medicines are not effective then allergy shots.