The best way to do any employee’s performance assessments is to do it up front: what are the results to measure, what are the behaviors expected to be evidenced, and what are the milestones / deliverables anticipated along the way? Assess as you go, adjust as required, and sum up at the end of the year.
It’s not how most people do it.
Most people collect thoughts after the performance period, and try to figure out what happened. For those folks – and you know who you are – James Neal has a book for you. Speaking Fluent Performance Review is advertised to give you all the catch phrases you need to plug them into your subordinate’s performance review.