I routinely compliment co-workers, usually by copying their manager. In fact I have a standing meeting once in a month, to reflect on the last month to see if I can send a thanks towards someone.
I read the title of this post and thought, it is obvious, that you let co-worker’s manager know the praise. It has some of the gems I didn’t consider, or think of like why one should ask first:
ask if it’s ok first
One thing that at least 6 different people brought up was the importance of asking first. It might not be obvious why this is important at first — you’re saying something positive! What’s the problem?
Giving someone a compliment that’s not in line with their current goals. For example, if your coworker is trying to focus on becoming a technical expert in their domain and you’re impressed with their project management skills, they might not want their project management highlighted (or vice versa!).