At the N4 level, you start encountering synonyms. This book does a great job of explaining the differences between similar words (like the various words for "wear" or "think"). It focuses on collocations —which words naturally go together—which is essential for sounding natural.
Would you like a sample weekly study schedule or an Anki deck recommendation for N4 vocabulary?
Shin Kanzen Master N4 Goi (Vocabulary) is a specialized JLPT preparation book focused on helping learners master approximately 690 essential words