Following are things that you have to cite, including an example of each and the reason why.
In Act I Scene II, Bevolio says "One pain is lessen'd by another's anguish." CITE IT
Why? The words are not yours.
Facts or ideas that you found in another source
The estimated population of Perth is 1,700,000. CITE IT
Alfred Russel Wallace thought he was the first to discover a gliding frog.CITE IT
Why? The facts or ideas might be true, but when they are not reasonably considered common knowledge, you must have found them somewhere.
Copying someone else's structure
If you say "I find these three elements to be crucial in understanding the sixth Cello suite." and John Doe wrote of those precise three elements before. CITE IT
Why? If you used John Doe's writing to find out about those three elements, or you know John Doe discusses the same three elements, you need to credit him.
Using collaborative research
If you reference research that you did with other people, CITE IT
Why? Those other people deserve credit too.
Paraphrasing conclusions, ideas and interpretations
When you paraphrase, avoid just mixing up the order of the original passage or keeping the exact structure of the passage and just finding synonyms. Use your own interpretation and CITE any references to the original.
Why? Paraphrasing isn't just messing with the sentence until it is unrecognizable. It means putting others' ideas within your larger context, while still atributing ideas and conclusions to their rightful creators