Expressing an opinion can be hard when it's not done in your own language. Agreeing and disagreeing can also be tricky as students can sound abrupt and communication might fail.
Below you can find a worksheet with useful expressions on how to express an opinion, agree or disagree.
For a full lesson plan have a look here: http://eltea.org/lesson-plans/lesson-plan-practising-expressing-an-opinion-an-agreement-or-a-disagreement-in-the-context-of-art