Mind the Line Calls and Be Honest
One of the golden rules of tennis etiquette is to call the ball fairly. If you're unsure whether a shot was in or out, give your opponent the benefit of the doubt. Honesty is key in tennis, especially since not all matches will have a line judge. Make the call confidently but be open to discussions if there's a disagreement. If you're playing doubles, allow your partner to make calls on their side of the court, and keep your focus on your own area.