How To Write A Letter To Someone's Boss Praising Them . Don't wait too long before offering praise. Take a few seconds to express your appreciation for your sales teams’ labor. Thank You Letter To Mentor 9+ Free Sample, Example Format Download from www.template.net Appreciation letter to boss format. I’d like to thank you, most sincerely, for all of the help you’ve given me since my hiring at xyz company. Compliment generously but not excessively.