Using a powerpoint or flipchart, introduce your students to the unit vocabulary for whatever topic you are studying in class. Make sure each word has a picture to go along with the meaning of each word. As you introduce each new word, discuss what it means, and give examples. Then, have students create a hand motion to go along with each one. The pictures will be helpful when the students are creating their hand motions. It's important to let the students come up with the hand motions as a class. Try not to give them too much help in creating those motions.
You can even make a game out of it! Call out one of the vocabulary words. Students must demonstrate the correct motion. If they do it incorrectly, they must sit down. Continue until one student is left standing. If you narrow it down to a few kids who just can't seem to mess up, get faster! You're bound to trip one of the up.