Focus is to the mind like strength is to a muscle. It must be trained over time.

1. Simply being in liturgy, recalling your mind to the service, will train it.

2. The Jesus Prayer as a general practice will strengthen one's focus.

3. Less screen time, as screens actually train one's ability to focus on the opposite way, by rewarding it for wandering.

Of course, people's attentive power varies, some people quite a bit, but everyone struggles at least a little.