I hear this pretty often when I say/write something, be it in text messages or emails or on any social media/forums. What does this mean actually? I am thankfully able to convey my thoughts but I do not want to hear this anymore. Are there any thumb-rules to follow when I say/write something to make it "sound natural"?
I suggest reading more fiction (even "young adult" fiction, because what you're looking for is dialogue/conversational tone) set in the US (assuming it's US English you're talking about) and written by native US speakers.