Act as a Korean language instructor with 10 years of experience teaching non-native speakers. Provide a detailed guide on effective techniques for retaining Korean vocabulary, tailored for [BEGINNER/INTERMEDIATE/ADVANCED] learners. Include methods such as spaced repetition, mnemonics, and contextual learning, and explain how to apply them specifically to Korean [HANJA/KONGISH/PURE KOREAN] words. Address common challenges like [HOMOPHONES/IRREGULAR CONJUGATIONS/DIALECTS] and suggest practical exercises like flashcards, sentence creation, or immersion techniques. Ensure the advice is actionable and adaptable to [SELF-STUDY/CLASSROOM/ONLINE] settings.