How to I incorporate critical opinion into my coursework?

Start by reading whole works - or extracts of works - by critics. Having a bank of quotes won't prove as useful to you as you'd think, and you'll have a hard time forming your own opinion around them.
There are a few ways you can treat critics in an essay, and doing some of all is preferable.
1) Using a critic to back up a point you've already made. This is fine, shows you're aware of the critical contexts of the literature you're studying. However - don't think that dropping in a critical quote which is in agreement with your point is substitute for giving an example from the text as to why you think that!
2) Using a critic as a spring board for your own point. This is good, if you can take a critical quote and then prove why it is correct, using evidence from the text. Taking the critic's idea further is always preferable.
3) Disagreeing with a critical opinion. This is great, if you can take a critic's idea and suggest why it is shortsighted or misguided. This shows complete independence of thought. However, as ever, remember you can't just contest a critic with no evidence. Always back up your idea with evidence from the text!