Do not write more words than is required
While answering the completion tasks, do not use words that are not essential. So, for example, if the word limit is three, you must not write more than three words. This is a mistake that many students make. In many cases, the correct answer may contain fewer than the number of words given in the instructions.
Use the same words given in the passage
Some completion tasks may involve words taken directly from the passage. In this case, try to use the exact same words from the passage. Think about the grammar and the meaning. If the word given in the passage is an adjective, you are not supposed to change that into a noun or verb while answering the question.
Pay attention to meaning and grammar
Some completion tasks may have options given in a box. Read all the options carefully. Since options are more likely to have the same grammatical structure, it may be possible to complete the given sentence with more than one option. You should give more importance to meaning than grammar while answering this type of questions.
Consider all options and then choose the one that makes the most sense. You also need to ensure that you have not used the same option twice.