Following Answer is written in short answer format. Actual conversation done would of course be much more plosihed and structured.
Use sandwich method. Highlight positive points and then come to improvement points.
Set the expectations clearly for their role, Provide examples wherever needed. For junior roles it will be more specific and for senior roles it can be slightly open ended.
Take actual examples, Be data oriented in the conversation rather than giving opinion that lack the foundation.
Highlight between what happened vs what could have been a better path.
listen throughly with an intent of improvement and not make it about mistakes and what they did wrong.
Listen and help the them identify what approach changes are required.
In the end highlight the points existing string points again and end the conversation with action items