Draft Pick/Ranked, what determines pick order?

First, I play a lot of games. The last week, I have been put 4th or 5th pick almost 95% of my games. Even though I ask nicely to play one role or another, someone outpicks my role. This usually ends up with the team having poor composition and we end up losing.

So, my question is, what determines what order you are in the pick? Why am I seemingly always 4th or 5th in pick order? It is fine once in a while, but with as much as I play, I find myself down on the bottom more than anything and it just doesn't seem like it is working properly.

Is there something I can do to be listed as top 1, 2, or 3rd pick more often?

Thanks.

EDIT, oh, then when I end up getting 1st pick, that rare occassion, someone almost all the time dodges. Then the next game, I am down on the bottom again.