I recommend two books on this topic:

Douglas Stone – Difficult Conversations

William Ury – Getting Past “No”

The first book speaks generally about how and why to give candid feedback. The second book is the second of Ury’s more famous book “Getting to ‘Yes'” but I think the more valuable of the two for how to set up and have particularly difficult conversations.

I have NEVER regretted giving someone a “tough” evaluation and the associated performance feedback. 100% of the time that individual made significant improvements in performance after some “tough love.”

I have a 50/50 record on the times I second-guessed my better judgement and “softened” a performance evaluation. 50% of the time the individual rose to meet the potential I wanted to believe they were capable of achieving. 50% of the time the individual continued their disappointing performance reinforced by a evaluation they didn’t truly earn… And those bother me so much on so many different levels, I never stop re-living those decisions. The duty of a leader is to make the hard decisions, say the hard things all for the good of the organization.

~Jeff