This is in fact a simplified version of a longer activity my students love (which I'm also explaining in the worksheet). In fact you can use it as a warm up before any lesson, and it works especially well for the last minutes of a lesson when students are starting to feel tiresome.
Procedure: 1. Write some words or expressions you want to revise on the whiteboard (you can also tell the students to look at the words appearing in two or three exercises in the textbook.) Use vocabulary that either is going to appear or has appeared during the lesson. 2. Tell the students to choose a word or expression each, but every row is going to be a team, so they should make sure every student in the same team has chosen a different word. 3. Explain that you are going to say a word at a time and, when a student hears the word s/he has chosen, s/he must sit down. The first team with all students sitting down wins. 4. Make sure you read all the words aloud so that they know how their word is pronounced (otherwise they will be expecting something else and will not sit down when you say the word.)
TIP: Depending on the type of students you have, you might prefer to prepare some scraps of paper with a word on each, put them facing down on your desk and then pick up one at a time. But if you do not have the time or just suddenly feel you need a lesson-filler, this is a perfect activity you can improvise at any time because it does not require hardly any specific preparation.
Objectives: Apart from revising vocabulary or preparing their brains for a new EFL year (or just a new lesson), The aim is training them to hear the vocabulary, because they often pick up the habit of reading words as they would pronounce them in their mother tongue. So, they are improving their listening skills (and, hopefully, their pronunciation, too.)