A trick to help you get that S rank for those important crates.
The picture explains it all. Farm. Farm is a really important stat that can be the difference between you landing that crate grabbing S and a B+. And while having a massively high KDA, like 20/0 does increase your chances of getting that S, chances are, you're probably not gonna reach that high of elo every single game. But what is it that you can fix every game? Your farm/CS.
I had one game with some friends in Summoner's Rift where I went full AP alistar mid. My friend with Nami and my other friend went Quinn.
I ended with 10/3/10, Quinn had 13/2/9 and Nami had 7/1/13
Quinn got an S+, Nami got an S+. But I got a B+. I was flabbergasted. I couldn't figure out why even though I had such a strong game, that I only grabbed B+ while the others who were also having great games, scored so much higher.
Then I looked at my farm. At 27:16 my CS was a lousy 81 with only 10k gold. Whilst Quinn at 244 CS and 15K gold.
I do not know the exact percentage that your CS goes into the S rank, but it does make a huge difference.
Even if you lose the game, you can still get an S if you have a nice KDA and great farm. If you lose and you still have a record of 15/2/20 with 240+ CS at 27 minutes, chances are you're still going to get that S.
TL;DR, Don't die, install farming simulator 2016, keep a positive KDA. Good luck you guys! :D