S rating system helped me to improve my game play amazingly.

Just in 10 days I went from Silver 3 to Gold 3 as Zilean support. After-game Rating system helped me to understand of what requires to become a better player. To achieve the highest ratings I had to stop following my team mates in meaningless invades or objectiveless team fights. In other words, if I don't support useless fights, more likely my team mates by not having backing will not even go on suicide attempts. Then objectives, objectives, objectives. If I see that two teams are grudging, let's say in the middle lane for a prolonged time, I just go for split push - it distracts opponents and forces them back while my team mates will have an upper hand in the mid. Every single time giving a hand to do dragons or sometimes killing scuttlers myself if a jungler is unavailable to do so. Never leave towers unattended, as Zilean I can speed up to cover my team mates if they can't present their lanes and push back the creep.

In conclusion - don't follow the pattern of your bronze/silver team mates. Do what is best for your personal rating (that represents good play) and ... objectives. Currently I get S about every third game (including loses) and successfully climbing up.