Teaching a dog to focus is behind all exercises and disciplines. It
has to be trained for like everything else in incremental steps.

Just like stays etc the dog must learn that it is rewarding to look
at you or concentrate on the exercise; the alternative is no reward;
thus what how you reinforce the desired behaviour is very important
as the dog may find that not focusing is more rewarding!

I specifically teach my dog and others to focus on the handler
whatever the distraction and build up distractions and heavily
reward those that are ignored.

If your dog is very easily distracted then it demonstrates that the
handler is either very boring (sorry) or the dog may be stressed and
exhibiting "avoidance" behaviours.

Not sure if that helps?