The meaning of the Liturgy comes from the service itself: worship, Scripture, offering, and Communion. The visible movement of people around the edges of the service should be interpreted with charity and reverence.
What is the better practice?
If you are able, come before the Liturgy begins. Arriving early helps you settle, ask for help, and understand the flow. It also keeps your entrance from becoming a distraction during the readings or Eucharistic prayers.
If you need to step out, do so quietly. Parents with young children, elderly parishioners, and people with health needs may have real reasons to move. Charity matters, but so does reverence.
Let all things be done decently and in order.
How to approach attention
Follow the best direction of the service itself. Stand or sit where you can pray. Keep your phone silent. If you arrive during the Gospel, Creed, or Eucharistic prayers, enter quietly and wait for a natural moment to settle.
When learning parish timing, the most useful question is, “When should I try to arrive next time?” That keeps the focus on prayerful participation rather than on judging what others are doing.