You cannot just give an activity sheet to students and expect them to complete it. These points are very important:
They have to know what to expect and to have seen a physical representation of the activity before they start.
Do not try to explain the activity, demonstrate it. For a worksheet type activity, this simply means doing an example (of the same type) on the board.
Elicit (get the students to tell you) a correct answer from the group to check understanding and do all of this before any material is given out.
For longer communicative activities, do the activity with a student (who will understand it) to show the group how it works. For example, if it's a game, then play it while the group observes.
Always check understanding before you start by asking students what they are going to do.
Bear in mind that the 'Do you understand?' question is largely redundant, as it doesn't tell you anything real about their understanding.
