In the beginning of our preschool day I have added a morning message. I write a simple sentence on our big dry erase board and then my daughter reads it and copies it down. This has also been the start of us discussing end punctuation and her learning that, as well as the obvious honing her writing skills. Here's one we did the other day.
So I wrote "Yoda is cute" and then we read it and I told her I was going to put a period as my end punctuation and explained why, I also showed her what it would look like and what it would mean if I did a question mark or exclamation point. So then she copied it and decided to put an exclamation point at the end.
Here's a few other simple sentences we've done to give you ideas:
"I love you!"
"The fish swim."
"Baby likes to swing."