I came to league from WoW where I was used to my hand picked, top tier raiding members and I had a hard time adapting to being matched randomly with people that I very little, if any, time to evaluate their strengths/weaknesses/personalities/etc and that they couldn't necessarily be counted on to know or do a specific thing. I felt extreme pressure to prop up my team because that was my role in WoW. Which often left me very frustrated in league, especially in games where I personally fell behind. If you have a mentality of "I have to carry my team" you are going to be frustrated, a lot. Focus more on just "doing your part". Focus on getting your 20%(you are 1/5th of the team) in above all else. So when you start falling behind instead viewing the rest of the game as an impossible mission to carry everyone from behind you see your 0/3 score so maybe you are only giving 15% and you just need to close that 5% gap.
A term I use a lot when im with my friends and someone behind is "stop the bleeding". When you are losing that is the #1 priority. I both hate and am terrible at ADC, I would rather not play league than play a game as ADC. I can't remember exactly how it happened but I ended up ADC in a ranked match and as expected, did horribly. I got to 0/3 and I was literally on skype chanting "stand in the back shoot towers" the rest of the game and we ended up winning anyway.
Another thing that was hard for me to accept is that you are going to lose about half of your games no matter what you do.
The biggest thing you can do to deal with tilt is to work on identifying it as early as possible and make sure you don't queue for another game until you are balanced out, whatever that entails for you. Go watch an episode of scrubs. Go for a walk. w/e.
