The specific techniques for how to give good feedback have been discussed at length by designers much more skilled than I am. However I have one small technique that I've found very useful in helping build positivity in a group:

I give positive feedback in writing, so people can read it over and over and feel good about themselves and really obsess over those positive words.

I give negative feedback in person, so it softens the blow, I can adjust what I'm doing on the fly and we can move past this uncomfortable situation quickly.

The only time I start giving negative feedback in writing is if I feel a need to start keeping track of each time I gave you negative feedback and it doesn't seem like there was much of an improvement.

That's all I got for today, bye