As far as I'm concerned, I usually begin the lesson using brainstorming techniques to introduce the topic.
For example to introduce the theme of friendship, I ask some questions such as:
-do you have friends?
-what are the qualities that you like in your friends?
- who is "the true friend "according to you?
the students' answers are meant to elicit vocabulary items related to the topic of the lesson.Here i will jot down students' answers in a spidergram to elicit words such as loyalty, honesty, sharing, help,...
the same topic can be introduced via a song ( students listen to the song and guess the topic or message of the song) or you can use wordgames and fun activities especially with young learners.
I hope that this will help you.