PSA: Don't Teamfight if Your Comp isn't Designed for It!
Title. If you have a really bursty, squishy team against a team with 3 tanks, 2 of which have hard engage, and 2 hypercarries, don't 5v5 them.
Play to your strengths. If you have Xerath mid, Caitlyn ADC, Jayce top, and Nidalee jungle, use your range and poke advantage. Please don't fight other teams in situations where their comp is designed to excel.
That is all.