How do i get an S

so it occurred to me that i still do not know what it takes to get an s on a champion, i have gotten plenty of them but how... i was wondering if there are guide lines that anyone know of that can show me where i can improve or if riot has thoughts on or is interested in possibly implementing a system where it shows you what it takes to get an s. I've been told that it is based off of how well your community does with that champion... maybe in the post game there can be a tab where you can look at the statistics of the champ you played to see where you need to improve to get a better rank. if anyone has any thoughts that can answer my curiosity please let me know or if you agree up vote so maybe riot can answer this as well.