Step #1: Know what you’re talking about. Never argue with people without fully understanding the topic, because then you just look stupid. Sources never hurt, either.
Step #2: Research the other side of whatever you’re arguing. Knowing what the other person will say will help you strengthen your own side.
Step #3: Never raise your voice. It just makes you seem unprofessional. I know it’s frustrating sometimes, but you’ll look less legitimate if you lose your temper. And people are less likely to listen to you.
Step #4: Know when to quit. Sometimes, you’ll be arguing about something that is irreconcilable. Better to just agree to disagree than letting it end in a holy war.