So you've got your twenty selections. And you've got twelve weekends before December. Which means you've got two letters a weekend to get out beginning Saturday.
Your list will be revised, maybe expanded. But what you want to include covers seven points of expression:
1) The person's name. I know that this is a minor detail, but it needs to be spelled correctly. If it's spelled incorrectly, it's a major detail.
2) "I'm writing this letter because," and state your reason. Think of why this person is important to you, and say it. After the "because," put your reasons of inclusion down on paper.
3) Reasons tend to be in a few categories: length of time in a relationship, history of friendship, events shared, support given, incidents of assistance, laughs shared, tragedy weathered, and sustained periods of closeness.
4) An explanation of feeling. Doesn't have to be long, and it doesn't have to be "when I'm with you, I feel...." That's not only not even worthy of a form letter or a bad poem, it'll make things awkward. Try this instead: "I always feel (safe, happy, content, humbled, supported, etc) when we're together.
5) Say exactly what they have done for you and how they make you feel: "When you've (shown up, supported me, continued to be my friend) I've always felt (important, valued, hopeful, calm, happy) is a good place to start.
6) Let them know how their presence in your life has made your life better. Actually, use that line. "I am better for having you in my life" is a great thing for anybody to read.
7) Let them know that you want them to continue to be in your life to share the same things you did this last year.
That's pretty much it. It doesn't have to be complicated. But it should be done. I have written letters because I think feelings need to be expressed. So should you. Life is increasingly short.
A lot of people have left my life. Hundreds of clients I'll never see again, friends that have left my life, and those that have died. I'll never have to feel regret about not expressing myself to them, letting those people I loved how absolutely important they have been to me.
And if you follow these points in the weeks leading up to Christmas, neither will you.