Leagues ranking system

So I need help figuring out how the ranking system works because last season I literally won 1 out of 10 placement matches and got placed bronze 2.. An yes go ahead an laugh or attack me for this, but this season I just finished my placement matches an won 6 out of 10 games an got placed bronze 3.. I have no idea what I'm doing wrong or if it got harder this season but I feel like I should of been placed higher then bronze 3.. All of u haters can make fun of me for it but I wanna know how I can better myself inside the rift.. If someone could help me with this I'd gladly appreciate it..