Now in the music industry, we often have this perception that professionalism doesnt matter. Our image of a musician is that of someone who is erratic at best and completely disorganised at worst. Musicians are seen as indulging in a lot of drug use, they're thought of as unreliable, and given they have a flair for creativity they're assumed to not be so good with left brainded activities, that is to say keeping themselves organised. Often the cultural stereotype is such that people think of musicians as people who have to be managed in order to get a desired result. The workspace of such a person might look like the following picture.
However there are a mutitude of problems with this approach. For example, there may be aspects of making music that seem less interesting to you than others, particularly things like establishing a web presence, replying to emails and the like. However these things are what require the most professionalism, and unless you have the backing of a label and a manager, these are things that you will likely have to do yourself. The catch is that you won't get to the stage where you have the backing of a label and a manager without some professionalism in establishing a web presence and replying to emails or just generally making connections in the first place. This means you need to learn to behave in a professional manner. Treat people with whom you're dealing with as if they were a client or customer.
This involves replying to emails in a timely manner and not just when you feel like it. It also means sticking to due dates. It means practicing your live performance as much as possible and aticipating any problems so that everything runs smoothly and the promoter you're dealing with will want to book you again. It means providing people with a press kit containing all the relevant information they might need when they make an enquiry. If you go the extra mile when you are dealing with people and you prove an easy and reliable artist to deal with, people will choose to deal with you over others.