How do I do a subject by subject comparison

For comparison, you need to write about similarities and differences.

Similarities

E. g. You can compare the nutritional benefits of dairy milk versus plant-based milk. Both milk provide nutrients in vitamins and minerals.

Differences

E. g. Research has shown that dairy has been known to cause cancer. Support with evidence: Many actors and actresses minimised or completely eliminated milk and dairy products from their diet. Studies also show that drinking plant-based milk reduced the risks of cancer because ...

Therefore, (you need to choose which subject is better).