Well, I don't know if you noticed what's weird with this question. One would never ask "how to become professional ballerina" or "how to become professional physicist" You go to school, spend years of your life learning and then you become one (if you don't change your mind and switch to something else). Yet becoming photographer (model, blogger, etc) somehow looks different. We see plenty of people who buy a camera and immediately start to call themself photographers. It's like buying a pen and calling yourself a poet, only a bit more expansive.

So the threshold of becoming a photographer is very low. As a result it's very hard to land a client (or even collaboration) when you are starting. Look at most of "Looking for a photographer" announces online, in 99% there is someone who will reply "I will gladly do it for free" (see question #2 in part-3). Or maybe it's you who's replaying that -  you want an opportunity to learn, build your portfolio, get some recognition. The news is, doing this you are collapsing the market for your colleagues trying to "make it". At least in "price only" competition.

So we stablished this: because of a very low threshold of entering the profession, you can't be a professional photographer if you compete based on price only. You have to offer quality that's much higher than one can get from a newbie.

To do that you need to take a page from physicists and ballerinas book and allocate some time to learn the profession. 2 month? 1 year? 5 year? Depending how hard you work and how talented you are, but usually 6 month to a year should do it - to get first clients based on quality, not to reach the peak of your career of course. At this point you are ready to do what engineer student does - take some work on the side while still learning.

After working like this for some time, say 2-3 years you are ready to "graduate". You didn't finish an art-school (and the ones who did will always be scary competitors), but you know technical part to a point, you work on manual, you know how to work with studio equipment, batteries, reflectors, smoke machine. You know light so well you became intuitive with it. You also established your own style and have plans on how to develop it further. Finally you start to have first returning clients, who pick you not based on price or technical quality, but based on your aesthetics.  

Now you need to make a last step to become a professional photographer: either get a job (model agency, magazine, other photographer's enterprise, etc) or become an entrepreneur. First road is good as long as you still have time to experiment and grow, during work or outside of it. Second road gives you more freedom, but also means you need you will need to go deep into business stuff. It means for 1 hour you will secure to do your work you will need to spend 2 hours on building and promoting your business, meeting prospect clients etc, at least at the beginning.

Even after couple of years you will spend 50% of your time looking for clients and interacting with them, 50% actually doing your job and 50% to do free work for promotion or to experiment with new things ( = invest in your future). Did you notice we have 150% in total? That's right, you will need to work a lot, much more than you would for a normal office job. Do you like photography that much? Then welcome to the club :)