Here is an example you can use:
Dear (Teacher Name),
I am very thankful for my family, and for my friends and relatives and everyone in my family. I am also very thankful that I am healthy and happy, and that life is great. I am very thankful for my friend (name) , who just had her birthday a day ago and gets to live more years. I am also thankful for my boyfriend (name) who is sweet and nice and funny and helps me with a lot. I am also thankful for my parents and god who has taken care of me since birth and loves me to death and i love them as well. I am also thankful for my brother and sister who are very annoying but i know they love me no matter what. And i am thankful for school, because I can use the knowledge I gain from school in the future and I can excel further. Thank you for taking the time to read what I'm thankful for.
Sincerely, your name.