Always repeat your customers order back to them.
Quite often as a waiter takes an order, the person ordering has just bit into a bread stick, or perhaps they are just a low talker. Sometimes they are neither, but insist on looking everywhere but the waiter that they are talking to while they are giving their order. This can lead to a misunderstanding and confusion about what they have ordered.
Repeating their order back to them gives you a chance to confirm what you have written down. A chance for them to correct you if you heard them wrong, heading off any mistakes that might happen. Taking this one extra step during the ordering processes can help prevent the appearance of sloppy service, and hopefully, improve your tip.