Use your own words and develop your own writing style
Many students, particularly when they first start writing, find it difficult to develop their own writing style. When you are reading and researching for a piece of written work, try to use your own words in your notes to summarise your reading, and include your own ideas and comments on each text that you read. As you practise and establish your writing style, you will become more confident about expressing your thoughts and ideas in your own way.
If your first language is not English, and you are not yet completely fluent, it can be very tempting to borrow a well expressed sentence or even a paragraph from another writer. However, this is plagiarism, and lecturers would much prefer to receive a piece of work in your own, if imperfect, style than to read chunks of text in perfect English that are clearly taken from another writer.