How do you write a thank you letter to your boss for all the help when he is leaving from the organistaion?

it's not so different from any other thank-you letter.if you're not very confident you could buy a thank you card which only leaves a small space for your message.it's the thought that counts-you gone to the trouble of marking the occasion.say how helpful he's been,why you appreciated his help/advice,wish him good luck in his next post,say you'll miss him for his positive contribution.