The ideal praise-to-criticism ratio is 5:1.
That is, every time you provide criticism (ideally in a constructive way), you should provide 5 positive bits of feedback.
This applies to everyone you work with: peers, juniors, people more senior than you and even clients.
Take the time to notice the things that they’re doing and the effort they put in.
Then tell them that you’ve noticed. And say thank you.