Is there a better way to say "ensure high attendance?" I thought about "ensure excellent attendance," but that didn't sound right either. The essay I'm writing isn't very formal, and the latter doesn't match with my tone. I'm saying the phrase in the context of ensuring high attendance at a presentation.
According to the Online OXFORD Collocation Dictionary, the positive adjectives that go with attendance are good, large and record.
Of these three, I believe large is the most suitable for your intended use (I suspect good attendance refers more often to a person than to an event).