Water temperature: always test with your elbow or a bath thermometer, aiming for around 37–38°C — a baby’s skin is more sensitive to heat than an adult’s, so "feels fine to your hand" isn’t always a reliable test.
Never leave a baby alone in a bath, even for a few seconds, even in a supportive bath seat — these seats are a support aid, not a substitute for hands-on supervision.
Have everything you need (towel, fresh nappy, clothes) within arm’s reach before you start, specifically so you’re never tempted to leave to fetch something mid-bath.