How to win ranked games?

Hey everyone. So ever since the new season came out things have been looking great. A big plus is that you can choose your two roles that you would like to play the most. I started playing ranked in the preseason and after my placements i got silver 1. Because it is the new season i don't want to fail my placements. So far, i have 1 win and 1 loss. My question is how do you win ranked games in your placements and not get demoted in your league? When you are in your league, how do you rank up without duo queuing? Like most people i am always trying to improve. Also do any champions preform bad or is it the summoner? Is there such thing as the best champions in ranked or can they all be good? I have also herd a lot that there are some sort of "objectives" in league. What are these? Thanks!