Git gud.
Heres how you win.
Don't worry about what your teammates are doing early game. Worry about your lane. You can't control them, but you CAN control yourself.
Using my Poppy play as an example. Typically, I will shit on any top laner I can come across(exceptions being Quinn, Darius, Malphite.) and if I don't, I can usually play defensive enough, warding correctly, and last hitting at my tower to avoid dying.
Next off, pretend you don't have a jungler. Don't play around a mindset you have someone who can help you or save you when things go bad. If you have your buddy pinging in to gank, work with them, but don't rely on them.
If im playing top lane, I will almost always have TP, we'll say you're a top lane player for that sake. Always keep an eye on your map.
If you happen to notice your bot lane, or mid lane has someone diving them, or shoving hard at the tower, you can TP in and pull some super hero shit. Try to do it from behind though. Otherwise you could end up wasting your TP. Mid laner, work your way down and play PJesus. Bot lane team, just keep farming. Get to Hyper Carry status ASAP. You'll cause death later. Support, you can wander a bit and make the mid lane fights a little more fair or sneak top lane, just don't abandon your carry if he's in a bad spot. It wont end well.
Teamfite time.
Beef cakes in front, Squishy scary people in the back.
Top lane Popples, I'll be looking for wall slams as much as possible and openings to make a jump on their scary guy for follow up. I'll also be looking for chances to play some Hot Shots Golf and sent their team as far away from the team fight as possible so we can kill their now exposed back line. In the reverse if we're at a disadvantage, play reactive. Hole in one their front lines when they come at you. Some pro plays, dive the enemy carry and ult the enemy front line from behind. Makes for some sick plays and one "Where the fuck did I just go now?" from the enemy team.
For everybody else, pretty much the same deal, just not as descriptive. If your team is on a serious defensive, but you're big and scary, play reactive. Theres no harm in letting the enemy team make the first move if you can turn it around. A scary mid laner can always pop behind enemy lines and delete the scary guys if they engage hard, the ADC can always kite the enemy front line away if your team didn't make any reactive moves, just keep yourself alive. On the flip side, if you can catch out an enemy squishy doing dumb things, capitalize on it, more often than not, your team will follow though.
If you can't get your team to follow up, or they're in total pissy pants mode and willingly goes around to screw you over, that game was lost long before the nexus exploded. I've had multiple games like that, just move on.
Heres some videos to watch.
https://www.youtube.com/watch?v=-bohs9D4h2k - From 2013, but still very valid.
https://www.youtube.com/watch?v=5PwPWdd-3bo- same guy, video about a year old. solid advice.