If you want to be taken seriously in this game you have to think and act seriously. If you can look and act like a professional writer then people are more likely to take your writing seriously. If you don't take yourself seriously, how can you expect anyone else to?
This may be pertinent advise, but what does a professional writer look like? There are a lot of them about as diverse as JK Rowling, Val McDermid (sp.), Terry Pratchett, Celia Ahern - like chalk and cheese, all of them. I think you have to find a level of professionalism that sits easily with you. We are all different in appearance, dress sense and personality. It's not good pretending to be someone that we are not as we will soon become uncomfortable and someone will catch us out! We don't want to be someone else but but want to try and take on board some of the writers' that we admire good qualities. What is about successful writers that makes them that way? What can we learn from them? What can we use from what we've learnt to enhance our own writing and professionalism?
It's a lot to think about but something that deserves our attention if we are keen to increase our chances of publication.