What has turned more certain losses into surprising wins than any other strategy I have found thus far is learning how to peel. Back in bronze, players learn the importance of focusing squishy carries and will often try to dive and assassinate them. While this may work if you have a fed assassin, those are extremely rare on the loosing team, especially in the current tank meta.
That said, consider this situation.
Your team is:
Top: Jayce -- Fairly fed, deals the most damage on your team
Jungle: Elise (you) -- Neutral KDA, strong enough to assassinate a squishy and third-health a bruiser
Mid: Cassiopeia -- Not fed but able to deal very good DPS
ADC: Ashe -- Not fed but able to deal decent DPS
Support: Lee Sin -- pretty tanky, valuable for his utility
The enemy team is:
Top: Irelia -- Moderately fed, has good DPS and assassination potential
Jungle: Xin Zhao -- Extremely fed, has dove your team every fight this game and taken out your ADC, Mid, and sometimes Top
Mid: Katarina -- Not very fed but deals very good DPS
ADC: Lucian -- Not fed but able to deal very good DPS
Support: Alistar -- has AOE CC
Thus far, Fights have consisted of Lee Sin diving their carries which you follow up on, resulting in Katarina and Lucian Dying in return for your own deaths. After that, Irelia, Alistar, and Xin Zhao dive your team and make short work of them, often trading Irelia or occasionally Xin Zhao for Jayce and then cleaning up. These consecutive three for five trades have allowed the enemy team to push MId to your nexus whereas your team has only pushed to their inhibitor turret.
After seeing this, your tell your team to not dive their team and to instead peel. You save your stun for when Xin Zhao dives at which time you stun him and your whole team collapses on him , deleting him before he can ult. Then, Lee Sin removes Alistar from the fight by ulting him and Cassiopeia ults Irelia and Katarina, canceling Katarina's ult and allowing Jayce to fight Irelia. You and Lee Sin then chase Lucian, who gets ulted by ashe, thereby turning what would have been the end of the game for you into a five for zero, allowing your team to push to the enemy's last nexus turret, at which point they all fall back to prevent them dying to the now-respawning enemy team. Through implementing the same strategy in the next fight, your team is able to win the final battle 5 for 3 and you and Lee Sin push to win.
Remember: The most valuable target is not necessarily the squishiest; it is the one that targets your team.
Peeling is important.