The IELTS reading test is a vocabulary test. If you have a strong vocabulary, you should be able to do well.
So how should you develop your vocabulary? My recommendation is to do all 3 of these together.
1. Extensive Reading (40% of your vocabulary time):
Read A LOT. Anything is fine. You don’t need to check every word you don’t know, just try to guess from context. Aim for quantity, not quality. You’ll pick up new vocabulary in context as you do this.
2. Intensive Reading (30%):
Read DEEP. Read one article in a deep way. Pick apart all of the new vocabulary and grammar. The is the opposite of extensive reading. Here you’re going for quality, not quantity. You can use Newsela, National Geographic, or IELTS reading books for this.
3. Flashcard Study (30%):
Use a system like Memrise, Anki, Quizlet (all 3 are free), or whatever else you like. Study the IELTS decks they have on there. Also put words you learn from your own study into here.
Do all 3 of these things activities and you’ll improve your vocabulary in no time at all.