My students love this activity and I usually introduce it at the beginning of the year, although you could do this at anytime to get students to learn each others' names and a little bit about each other.
I start by giving each student a 3 X 5 index card. The students write their names and three facts about themselves they don't mind sharing with everyone. I collect the cards and read a few of them when we have a moment at the end of the day or are lining up to go someplace, etc.
I just read the facts, and the students try to guess which of their classmates wrote the card. After going through the cards once, I go through the cards again to see if we remember the facts about each person.
This activity encourages students to get to know each other, use each others' names, and make connections with their classmates.