Come, I will conceal nothing from you. On Heroes of the Storm and League of Legends, my in game name is Lucentile. You will see that this means in LoL that I am B5, with a 43~% win rate. I am what you would call "Terrible" at League of Legends.
But, you'll also notice, that over a long period of games, I've been consistently getting better. Over the last month, my average K/D/A has gone from something like 1/11/8 to something like 3/5/12. My CS is significantly higher. I make fewer weird build choices. I know my characters better, even having finally played enough Leona for the game to recognize me as a Rank 5 "Master" Leona. In Heroes of the Storm, I've got go-to builds for all of my characters, but I know how to flex build to counter things.
So, why am I getting better [besides just playing more and making better Rune Pages/Masteries?] Because I'm asking the right questions on how to get better. If you go to Summoner School on Reddit, you can find some posts I made there asking about the value of Sightstone, comparing boots options, etc., etc. These are actual, mechanical things that have helped me. Forcing myself to delay the Ruby Sightstone, and just sit on Sightstone, and to embrace Mobility Boots over defensive boots has helped me play better, which in turn, helps me help my team win.
Which brings me to the next thing I notice in almost every League forum I've gone to. Lots of people want to get better. This makes sense; part of the fun of a MOBA is getting better at the game and playing against tougher opponents to have better games in general. But, one of the biggest things getting in people's way to getting better is that they just ask bad questions.
Go to the Summoner School page on any given day. Right now, I counted about three or four threads that were about how to recover when your teammates feed, when other lanes lose, how to keep your team from throwing your lead [note that it is always that player's lead, not the team's lead], etc., etc.
Let me tell you how this question sounds to me, and probably anyone who actually plays at a reasonable level: "What do I do when I get stupid team mates who won't listen to my shining awesomeness? Like, guys, how do I keep these paint chip eating window licking potatoes from costing me games?"
And here's the answer: You lose. When your entire team is falling apart, and they're 0-10 as a team before you upgrade your machete? You've probably lost the game. It happens. Do you want to get better? Ask better questions. For example, instead of the whining about how far behind the laners were and asking for everyone to say "Sorry Jungle bro, I know how laners suck!" Maybe ask: "How can I keep my laners safe in the early game to survive early game ganks/pressure from opposing jungles and laners?"
Here's an answer for that. I jungle sometimes, and you know what I've learned? When I see that my entire team was made of bad laners who needed safe farm/jungle pressure, or people who got counter-picked that could use my help, I don't lock in Warwick and tell everyone "Don't worry, at 6 I'll gank." Doing that contributes greatly to the team's inability to survive the laning phase. And, despite what some late game champion is telling you, no, you cannot recover late game if the laning phase puts your team too far behind. If you have a late game comp, it is important as the jungler to ensure your laners can reach the late game without being epically behind.
So, if you have a hyper carry like Kog'maw, or someone with infinite scaling like Veigar, Nasus or Sion, who needs the game to last, or someone who needs your help early [like any melee top against a good ranged top], pick a jungler that can do that. Pick a jungler who can do something early to relieve the pressure you know your laners are going to be in -- ESPECIALLY in solo queue/Bronze. I know that my team will probably have one problem lane, so I don't pick junglers that have to basically abandon lanes until 6.
If you first pick as jungle someone like Diana or Warwick, you're setting your team up to have a bad day. Pick versatile, tanky junglers if you pick early who can gank at Level 3 if the opportunity presents itself. Xin Zhao, Udyr, Vi -- even Amumu or Sejuani if you can land their CC -- are all viable, good junglers that don't tell your team "You're on your own until 6!" Not only that, being a tank for your team eases the burden and the fact that some people are not going to tank, no matter what. Take the bullet and enable your laners instead of trying to be the jungle carry. If you see them struggling, deviate from your route and help them if you can do it safely. Take some Movement Speed (maybe go 6/21/3 if you're a tank, for example) to roam better. Try and start sharing Blue/Red early if you can; ward and scuttle crab on cooldown. Pink whatever buff is opposite your support, and ask them to pink the other.
This is all good advice that can help you keep your lanes from losing too hard. But, if you don't ASK for that sort of advice, you won't get it. If all I'm hearing is that you have bad teammates, feeders or AFK'ers, the only advice I can give is: Play more games until the RNG evens out, as it will if you are not a feeder/AFK'er/terrible, since after all, the other team is more likely to have those issues if you don't contribute to it to your team.
Ask better questions, and you can get better answers.