When your serve hits your partner stationed at the net, is it a let, fault, or loss of point? Likewise, what is the ruling when your serve, before touching the ground, hits an opponent who is standing back of the baseline. The answers to these questions are obvious to anyone who knows the fundamentals of tennis, but it is surprising the number of players who don't know these fundamentals. All players have a responsibility to be familiar with the basic rules and customs of tennis.
Read The Code.