Which grammar errors should I fix first to improve my IELTS score?
Prioritise errors that recur and interfere with meaning. Common problems include articles (a, an, the), subject–verb agreement, verb tense, prepositions and sentence boundaries. Do not try to memorise every grammar rule at once. Take one of your own essays or a transcript of your speaking, mark repeated mistakes and choose one pattern to work on.
Write several new sentences using the corrected form, then check whether you can use it correctly in a longer response. Accurate everyday grammar is more useful than complicated structures full of errors.