The best way to prevent anaphylactic reactions is primarily:
d) By avoiding things that trigger reactions.
It is essential to identify and avoid allergens that can lead to anaphylactic reactions. While having an epinephrine auto-injector (option b) is crucial for emergency situations if exposure occurs, it is not a preventive measure prior to exposure. Regular use of antihistamines (option a) and long-term control medications (option c) are not effective for preventing anaphylaxis since they do not address the severity of anaphylactic reactions. Awareness and avoidance of triggers remain the most effective prevention strategy.