Reliable Way to Know Most Popular Role?

While I'm sure we're all tired of hearing people complain about this, I strongly dislike the fact that I cannot choose a role and know for a fact that I am going to receive it anymore. Now it feels out of the question to ask for this attribute of the game to be removed, so I'm simply trying to find semi-reliable ways to get around it. So my question is as follows:

If I want to play top lane, and I lock in top lane as my "primary" choice, what should I choose as my "secondary" choice to better improve my chances of receiving the top lane role?

If the algorithm for creating teams and games proceeds intuitively, I would assume that if you choose a lesser played role, even as your "secondary" choice, it's more likely you will receive that role since less players are queuing up for it. So is there a way to know which roles are the most or least played at any given time?

As an aside, if a riot employee could explain how the system for creating teams works, I would greatly appreciate that as well (not only for practical use, but I find it very interesting).

Thanks to any and all who reply,

Diri