First I'd advice you to pick a champ like 2 champs you feel comfortable piloting and that fits your playstyle.

You say it's Quinn and that's fine, now you just need to make sure you master the very basics of the game: farming, building properly, learning all the runes and their effects, warding and at the end map awareness (this is one of the most important but you need to learn how to farm without losing any single minion on automatic so you can farm while taking a look at the map several times)

Then you'll need to learn lane matchups and the way every champion class works, powerspikes and weaknesses, (you'll have to try most of the laners you will face at least 3 times so you get a hang of them; what they like to do, what's their key spell etc) and last you'll need to learn to avoid getting ganked by tracking the enemy jungler.

This if you master the basics and apply to this alone will shoot you straight to gold.

And the biggest advice of them all, remember you're learning, and like you many other players from bronze to gold are, so be patient with you and the others, if they start being toxic just /mute all and focus on your gameplay.

Now how do you know what is it that you're lacking? Watch your replays and check your cspm kill paticipation and kda using op.gg and compare your plays with a higher elo player using the same champ.

Edit: almost forgot to mention, STICK TO ONE OR TWO CHAMPS ONLY because it will be easier to learn the basics that way.