If your vocabulary is weak, first decide what “weak” means. You may know too few words, recognise words without being able to explain them, understand them but fail to retrieve them quickly, or know them passively without being able to use them accurately in speaking and writing.
The repair depends on that distinction. Build breadth when too many words are unfamiliar; build depth when meanings and relationships are thin; practise retrieval when known words disappear under pressure; and practise generative use when vocabulary stays trapped in recognition. Learn words in context, revisit them over time, and make yourself use them rather than only reread lists.
Start with the eduKateSG Vocabulary Hub, then choose the route for the learner’s level. For the wider English system, use the English Learning Hub.