(These may be useful in any classroom or group setting)
So you want the students to make pairs, the easiest way is to have them work with the student next to them. Except then you end up with the same pairs all the time: students who dislike each other, students with vastly differing levels or even a pair who fancy each other and spend the entire time flirting (it happened!) You can turn this into a chance to get a little extra English in with these activities.
5. Half Sentences
Does exactly what it says on the tin. Write sentences and split them into half then have the students find the matching half. This works best if all the sentences follow the same grammar, "if" or "but/and" sentences are good for this. Warning! Double check there are no confusing sentences or multiple possible answers! When they find their pair they can sit down together.
4. Half words
Runs like half sentences but they each have a half of a word. This forces them to think about the spelling of the vocabulary. Japanese students at least have a tendency to try to see the word as a whole shape and guess it. Again double check for multiple answers!
3. Matching pictures
Give the students small pictures (of which there should be two copies) Make the picture be the answer to a question and have the students walk around and ask the question to find the student with the same answer. The possibilities are endless so long as you can have enough answers!
"What do you want to be?" "I want to be a doctor"
"When is your birthday?" "It's November 5th"
2. Line Up
Have the students line up in some sort of order, alphabetically or by height, how long it takes them to walk to school etc. Then either pair of the first two students together and keep going, or pair the first with the last and so on
1. Puzzle. Set some sort of puzzle or riddle on the board, or give the students some kind of task to do. The first students finished will pair up and so on. This is useful if you want to sort the students by level, but be careful not to make the lower level students feel bad. This depends on the atmosphere of your classroom and you know that best!
Last thought: What to do with that odd left over student? Either pair up with them yourself or make sure the activity can be done by three people. Either way make sure you consider this beforehand and have a plan!