For the first pick of the first tile, I think the game chooses randomly which player goes first. Then the rule is that you will pick the next tile according to how you chose the previous one. If your meeple is on the third tile, you will be the third player to choose your next tile. It's the rule of the material game too. If one turn you get to put your meeple on the first tile, the next turn you will be first to choose. If you put your meeple on the first tile again, you will choose first the next round. And so on.
That way, there is often a tactical choice to make : do you choose the tile that is most interesting now, or do you choose the first even if it's not the best so you can choose the best the next round ?
I hope it is clear.