Learn ALL the roles. Nothing worse than someone who "Only knows top - TOP OR FEED!"
Start with ADC. Learn to last hit and farm safely with range. Basic zoning with ranged AAs and you come with a babysitter not having to worry about engaging/peels. You're just there for the damage
Support next. Learn how important vision is and how to use cooldowns for trades and when to engage/disengage. You're just here for the CC & learning how important it is to abuse cooldowns for trading
3rd learn Top. Apply what you learnt from bot lane and bring it to the top where now it's just all you. Ward to stay safe, manage CDs for trading and while doing damage + CSing. If you're heavily relying on someone else (jung) as you were while duo laning, you have lots of room for improvement as something is still lacking in you that you need a babysitter. OMGWTF GETTING CAMPED is not an excuse to die/lose lane - thats what vision is for to not get ganked and waste their junglers time. Losing in trades - you can do better managing CDs and zoning
4th learn Mid. Once you've obtained sufficient experience to CS, ward, zone & manage cooldowns you can now be responsible enough to become a more important role as a carry, likely with cooldowns and less focus on basic AAs. After being able to manage not getting ganked from 1 path as top, you now have to watch many paths. Stop calling "MID" right as you get into lobby if you're newer/bad and know nothing about the game wanting to be the center of attention. Now you can practice on roaming and watching jungle more as you're mid and everything is closer to you in proximity if you need to move to another location.
Finally learn Jungle. Not only do you have knowledge on how all the lanes work now, but you have to watch all the lanes. If you see something out of place in that lane by learning that role, you can assist with it. IE- Top no wards - throw a ward down in his river bush so even if you dont gank he has no excuse for dying or losing super hard; Mid getting zoned - provide some presence around mid so the enemy doesnt feel as safe. Even if you take a chunk of their HP off on gank, they cannot zone your mid as effectively as they can be at risk of dying or ganked again.
Ganking and getting zoning power is BETTER than dying for a kill since no one gets ahead kill for kill, but if you get an upper hand you can force missed CS and attention for their jungler. Zoning, HP & mana of your laners becomes another resource you can manage as jungle - if theirs is higher you can throw your weight around to even it out or get it more ahead.
You're now also responsible for even more vision outside of lanes, manage respawn timers, manage your HP/mana to engage ganks, track unseen enemy movement based on jungle patterns (ie can estimate where their jungler is without even seeing him) and additional objectives none of the laners ever consider. You also have to better manage your gold as you have to complete your build while getting less income than laners, while having to stop farm to help laners in addition to buying items for vision control.
Once you get decent at the above, you can abuse power spikes based on when you get your items and when the laners get their items so you can get favorable skirmishes, which will not only award kills but further advantages with towers and dragon/baron. This isn't an AFK farm without having to worry about an enemy poke role. Lots of noobs want this slot to just farm passively without having to worry about fighting an enemy player - THIS IS SO FUCKING WRONG AND MY BIGGEST PEEVE.
Not saying you have to be pro at all of them. There will be one that you're better at and have more fun in but at least have 30-40 games in each before ranked so youre not a huge deadweight that becomes uncarryable. Everyone in solo Q thinks everyone else is BAD and want to be the "superstar carry center of attention I am the team I hold the team together mid" so automatically wants mid even if they dont know the basics mentioned. Any role can carry the team - dont think you have to be mid to do so