My students often say "I was looking at the TV" or "I don't watch", so I made this worksheet to help explain the differences. First it's a small-group activity where they tick which phrase they think you should use for each situation (page 2), then we go through the answers together (page 1). For a comprehension-test read out the questions on page 3 and get them to say if they think it's correct English or not. Includes the little-taught rule of watch vs. see for TV/movies (see is for public spaces such as the cinema, watch is for private places like TV). Took about 15-20 minutes with my 16 year olds and they seemed to enjoy it.
