Okay, first thing to realize is that you make mistakes. Everyone does. Learn from them.
Next step is to realize you're going to have a bunch of potatoes on your team that need to be carried. You need to PRACTICE PRACTICE PRACTICE until you are good enough at your role to absolutely obliterate your opponent.
I don't just mean win lane, I mean roflstomp the shit out of the other guy (or gal). Place wards and keep punishing him (or her). You are the only one who can win the game, so you HAVE to be fed as fuck.
A good way to do this is to play extremely easy, low counterplay, heavy carry champions. Examples: Annie, Master Yi, Fizz, Amumu. Trust me, in Bronze, NO ONE will know how to deal with these champions once they get rolling.
Here's a simple guide to each of them:
Annie: Farm with Q until you hit level 5. Don't worry about saving your stun until then. Once you get there, do a Q + W combo, then back off. Do it once more if you are able to. Then, THE INSTANT you hit 6, Flash onto them, Ult - W - Q - Ignite. You WILL kill them. Back, get items, and go all-in every time your ult is up.
Master Yi: Farm farm farm. Get Sated. Come out and outdamage every person on their team. They won't try to stop you because it's Bronze.
Fizz: Play safe until level 6. The INSTANT you hit 6, Ult - E - W + Q - Ignite. Again, you WILL kill them. Go all in whenever your ult is up.
Amumu: No one counterjungles you early, so farm until you hit 6. When you do, start ganking every time your ult is up. Build Runic Echoes, Sunfire, Abyssal Scepter, Rylai's Crystal Scepter, and Iceborn Gauntlet. You will outdamage everyone, yet be unkillable.
Finally, remember that some games are unwinnable. You WILL climb if you keep playing and practicing. Trust me. You are getting better with every win and every loss. It seems difficult at times, but it will even out eventually.