Hi dear AnnEe
Well, there are lots of different ways. The ones I mention here are a few that I have experienced myself in my classes.
1. Whenever I feel happy myself, I can transfer this positive energy to my learners as well.
2. Being fully prepared for the lesson you are going to teach, regarding some real objects,some games, some jokes ans some interesting things related to the theme of that lesson to zest up the learners.
3.Sometimes in some of my upper-intermediate classes I let them teach some parts( including vocabulary or some very simple grammar points that they have had so far such as: the -ed / -ING adjectives),of course I provide them with some handouts, some hints and suggestions. I always ask for volunteers. They really enjoy most of the time.
4. Have the students move in class rather than just sitting and talking in pairs or groups. I usually write the questions that they are supposed to discuss in groups on a piece of paper and stick it on the wall around the class and make them move in groups and talk in this way they do not depend on their book.Of course I determine who should be in the groups.
I hope they can be of use for you.