“Good job” slides right off. “The way you calmed that customer down was smooth” sticks for a week.

Vague praise carries no information, so there is nothing to hold on to and nothing to repeat. Naming the exact behavior tells someone what to do again, which is the part that improves things, and it proves you were watching closely enough to notice. People keep specific praise for a long time; the general kind evaporates on contact.

The next time you want to say well done, add what and when. One sentence about the particular move is enough. Give it soon afterwards, since praise attached to a memory works better than praise attached to a summary.