The best way to prevent allergy symptoms is to prevent your exposure to the allergens that cause the symptoms. If you have already been exposed, work to reduce exposure and decrease the symptoms.
Find out what you and your family are allergic to. Then purchase Allergy Products accordingly. If you know you are allergic to grass and you are going to a picnic on the next day, take some medication with you. If you know you are allergic to mold, do your best to avoid the basement.
If you have gotten prescription medication, take the medication exactly as your doctor told you to.
If you are using over the counter medication and symptoms are still persisting, go and see a physician.
Be prepared. Know when your allergies are at their worst and prepare yourself for them.