How do you practise gratitude meditation?

Settle first with a few slow breaths, then choose one thing rather than several, and pick it by where any warmth already is rather than by what you think should matter most. Name it, which takes about two seconds, and then keep going past the naming: the temperature of the moment, where you were sitting, what was actually said. The specifics carry the feeling and the feeling takes time. Ten minutes is a reasonable floor and longer is normal. If your attention wanders, return to the same thing rather than searching for a new one, because the searching is what makes the practice tiring.