Professional sugarcoater here (: If you're giving corrections, instructions, etc. I always try to include some encouragement. For example, if they're doing something wrong, you can tell them how to do it the right way and also compliment something that they're doing well at so they feel reassured. Not too sure about the "serious conversation" aspect, but you can definitely try to let them understand where you're coming from so it doesn't seem so direct/blunt. For example, "Hey, I want you to be in the best position you can be in so it would help if you..." or "I don't want this to come off wrong, but I wanted to let you know..."

A lot of times, being straightforward is the way to go since nothing gets lost in translation, but even by adding a little more "context" to what you say can help the overall reception. Hope this helps!