Some Tips

My tip for getting out of elo hell is to main 1 good champion. This way you will know the ins and outs of said champion and will not have to worry about not knowing the mechanics to a random champion. Secondly, if you win lane, don't sit in your lane and farm then complain ur team feeds. If you get a lead, roam A LOT, get your team a head. This way you not only put yourself ahead but you give your teammates a lead to continue to snowball. But be cautious and make sure that you don't throw. Happens a lot, just keep in mind to never do anything that might lead to you dying, even if it is for a kill, but just be sure to learn from your mistakes plus my lil tip and eventually you will get out of "elo hell".
Good luck in your future games!!!.
Based on my experience so far trying to be a OTP Twitch!

Pros:

You can learn all the nuances of your kit, and from that you learn a few tricks. This also helps you get a better sense of how to outplay others.

As the kit becomes more natural for you, you can spend less time thinking about it, and can now get a better sense of the macro game.

You get better at understanding matchups, and you learn them more quickly, since one half of the matchup (yours) remains constant.

You tend to be playing the same roles over and over, so you're not spreading your learning time inefficiently.

By getting more comfortable with a single champ, you start to see opportunities more frequently. I've also found that, for myself, I start to see where I could have done better in a situation that went sideways, and as such I tend to rage less against teammates for their mistakes.

All of this stuff leads to mastery, and this in turn usually leads to a better winrate.

Cons:

You're more vulnerable to drastic shifts in the meta, since you can't adapt as easily as others can by just switching champs. If your champ becomes flavor of the month, now you're more susceptible to having it picked by somebody else, or banned away from you.

If you can't get your champ, you risk struggling hard with a champ you're not comfortable with.

If your champ is only really suited to one role then if you can't get your role, you risk messing up your team comp, tilting teammates, etc. This shouldn't be a problem for Lulu or Gangplank, though.

If you're focused in on only a couple of roles, you lose out on understanding better how the other roles work. Coordination is OP in this game, and sometimes you can better learn how to coordinate by playing different roles, understanding what it is each role is trying to accomplish, and accommodating your teammates when you're in your comfort roles.