To enhance vocabulary for essay writing in UPSC, candidates can utilize various techniques such as reading extensively across different genres, maintaining a vocabulary journal, and practicing analogies and synonyms. Engaging with platforms that focus on word roots and contextual usage is also effective. Furthermore, candidates can enhance their skills by writing essays regularly and seeking feedback from peers. Tools like flashcards or vocabulary-building apps can serve as supplementary resources to solidify learning, ensuring a rich and nuanced expression in essays.