Is ranked a solo thing?

Depends on your division. The higher you are, the more teamwork there is. In lower divisions you have to step up and be a leader and call shots. Call dragon, call pushes, etc. It may not happen all the time but it helps. The one thing you have to do is keep your cool though. If you lose your cool, your teammates are less likely to follow you.

It's like DaCush said. Here's a small fllow chart for ya buddy. Bronze: Call the shots, Dragons, baron, sieges. (Don't be a dick about it.) Silver: Call the shots, Sieges. (Don't be a dick about it.) Gold: Cooperate with your teammates. Platinum: Cooperate, and get your teammates fed. Anything + Platinum I can't help you with.

You're given a chat box and pings to communicate with your team.

I feel the lower the division you are, the more you need to solo carry. If you're good enough, you should be able to easily carry yourself and win games pretty easily with whatever role you go with, er... as long as your champion has killing potential I mean. The higher you rise, the more teamwork comes into play because other players will recognize you as a threat and will GLADLY work together to stop you from making them lose. Ever been ganked by the Top lane, Mid lane, AND jungler with their ADC/support coming at you while in Bot lane? Well that's why.

By all means, if your team wants to work together, go for it. If you can make plays on your own, do that too. Do remember, though, that when you're losing or behind in the game, you can always make a comeback if you start working together as a team and they still have a YOLO mindset. If they keep that mindset for long enough, your team will be able to catch back up and even pull a win because of their overconfidence, though just remember that the higher up you go in ranked, the less likely they will either make the mistake or keep repeating it over and over.