Synonym and antonym questions reward a curated list over broad reading. Focus on words that recur: abundant means plentiful, benevolent means kind, candid means frank and diligent means hardworking.
For antonyms, learn in pairs: ancient and modern, scarce and abundant, transparent and opaque, frugal and extravagant.
When unsure, use the word in a sentence and test each option in the same slot. The option that preserves the meaning is usually the answer.