I mostly commend at random.

I only really target someone for commendations if they did something to really earn it.

Let's say I'm on a trial or raid fight and one healer keeps dying and the other healer is solo healing most of the fight, I may commend them.

If there's a newbie and someone is very helpful to the newbie, I may commend them.

If we have a near party wipe but someone saves the run, like a sole healer surviving to lb3, or someone soloing the last few % of a boss etc, I'll commend them. Consider this 'success during a crisis commend' category. If things get hairy but someone pulls us through, they get a commend.

Most runs of things I do however, I just commend someone randomly because nobody really stands out in most runs when things are going smoothly.