Some things I would recommend are:
(1) every day / before the exam:
- read, read, read. Practice makes perfect - and it's not a cliché, it really does!
- when you come across a new word/phrase, try to work out its meaning from the context before you check it in a dictionary. This skill will be extremely useful in the exam.
- study key vocabulary - if it's Academic IELTS you're doing, check out the AWL (Academic Word List) = these words are extremely common in academic texts and they always come back, regardless of the topic.
- when you study vocabulary, always make sure you know at least 2 synonyms for the new word if possible. Most questions in the IELTS want to check if you know many ways of saying the same thing
- pay attention to reference words, such as "it", "they", "those", "such", "the following", etc. They usually show relationships between words
- fast reading: (a) practise reading "in chunks" (not word by word, but trying to take in a few words at a time, e.g. a clause or a prepositional phrase) (b) timed reading - every day, take 30 lines from a random text, time yourself reading them, then cover and try to recall main points (c) make sure you are familiar with the skimming / scanning techniques; often you don't really need to read the whole text to get the answers to some questions
(2) in the exam / when doing practice exams
- be extra careful when questions contain words such as: "always", "every", "the most", "the only", "main", etc. Double check if the reason they're asking you, for example, is really the main reason, or perhaps only one of the reasons.