Many IELTS students become obsessed with 'linkers' - words or phrases that link ideas together in a paragraph e.g. firstly, secondly, furthermore, moreover. There is nothing wrong with using linkers, and they can certainly help you to write good paragraphs.
However, linkers become a problem when they are the only thing that students care about. Examiners care much more about the content between the linkers.
Here's a useful exercise to get you focusing on content rather than linking: Try writing a coherent paragraph without using any linking words or phrases at all.