In all seriousness, to become a pro you simply have to declare yourself as such when you register for a tournament.
Basically, irregardless of whether you played juniors events or not, if you want to play with the big boys you have register to get a IPIN with the ITF before you enter a tournament. Since you have no ranking, your best bet is entering the qualies of the futures event(s) closest to where you live and win matches in order to get points, which in turn you will then appear on the world rankings. You'll start out at about 1550 or so in the world if you manage to earn a point. If you are really bad (or not so great, depending on how you look at it) and have the finances to do so, it's a bit easier to go a 3rd world country to earn your points playing satellites and futures events there. You won't get direct entry into a futures event until you're ranked above 1000. Futures pay is so little you can't possibly live/travel off it, the goal is to earn enough points as quickly as possible in order to move up to the challenger level, which even attempting to qualify into those pays better unless you win a futures title. Basically unless you are from a wealthy family you either need sponsors or the support of your national tennis federation (USTA in the case of Americans) to be able to stay on tour until you get your ranking to about 250, at which point you are just about making enough money to support your career. Also your federation can help you get WCs into main draw and qualifying tournaments that your ranking wouldn't allow you to get into. It's the chance for your ranking to jump up significantly if you can manage to use your WC to win a match or two. Also once you start consistently winning back to back matches, if you reach the SFs of a tournament and you were the list to qualify for the next tournament the following week, you get a SE (Special Exemption) which allows you direct entry into the tournament without having to qualify. So there are great rewards for winning as many matches as you can in a row to avoid qualies and to increase your ranking and prize money rapidly. No player has "made it" without a coach, probably one of the biggest expenses for a starting pro, usually if you have 'talent' you can find a sponsor or your tennis federation to pay for your coach to develop you into a champion.
Before you ask, no I'm not a pro.