Aspirant – People studying for or taking the IELTS are called candidates. Aspirants is very old-fashioned.
Avail – One avails oneself of an opportunity; the reflexive pronoun must be used. One does not, for example, avail of a service. Note that this word is very formal and is used infrequently.
Clear – One passes an exam. One clears security, e.g., in an airport.
Doubt – A person who wants to make an inquiry or request clarification has a question, e.g., I have a question about last night’s homework. A doubt is sense of mistrust or suspicion, e.g., The police doubted the suspect’s explanation for his presence at the crime scene. You can, however, say that you have no doubts to indicate that you are absolute certain about something.
Fetch – One fetches a physical object; a student earns a grade.
Few – Almost none; indicates unpopularity. Few people believe it = Almost no one believes it.
A Few – Several, Some; indicates slight or moderate popularity. A few people believe it = Several people believe it.
Give – One takes a test/exam. One gives a person a gift.
Hence – Native anglophones use this word infrequently as a substitute for therefore. It is more formal and is only used to strongly emphasize that one is drawing a logical conclusion. In speaking or informal Task 1 letters, use so. In writing, try therefore, thus, consequently, or as a result.
Join – This is subtle, but one typically joins a class or event that is already in progress and signs up for or enrol(l)s in a class that has not yet begun. One can also join a team or a company.
Prepone – This word does not exist; use reschedule, e.g., I hope we can reschedule the meeting for next Tuesday.
Reach – This word must be used with a noun (direct object) immediately afterwards, e.g., It was almost 9 o’clock when we reached the restaurant. You cannot just say, It was almost 9 o’clock when we reached. However, you can say, It was almost 9 o’clock when we arrived.
Revert – One responds to or replies to an email. Revert means “return to an earlier version”, e.g., We’re having some problems with Version 3.0 of the software, so we’re going to temporarily revert to Version 2.0.
Trainer – One works with a trainer to prepare for an athletic competition; one works with a tutor to prepare for an exam.