ProTip - Regarding your own play Pay attention to what you did to die or get ganked, not the fact that you died. Realize you overpushed with no wards, or you all in'd at a bad time, or a certain champ just is strounger then you in the current situation. Your going to die just accept it. Learn from it tho, dont get mad. If you get mad your going to miss a valuable lesson that death just taught you. Be like "Ah I see, here is how I'll grow from that"
As for your teamates. Just dont give a shit. Really. What are you going to do. Bitching will make them play worse or quit, it wont actually make them better. If you see what they did wrong, try to respectfullly coach them maybe. Give them tips, watch their lane more and ping danger situations. Be helpful. If you get someone who really just doesnt get it, oh well. Its completely out of your control. You can still use the rest of a lost match to fine tune your own mechanics
ProTip 2- Take a break. If you lose, and even if you win, stop playing for a damned moment! Get up, take a drink, look out the window, refresh your psyche. Its healthy anyways. Let yourself regroup, and your last loss stop stinging a moment. Give yourself time to realize that its just a game. Take a deep breath, then go have fun with it