I am no pro but i have played over 300 games and would consider myself avg.
I would suggest to do what i did which is focus and learning to play one character really well and eventually you will learn the other characters.
I would also strongly suggest play lots and lots of Support characters until you find the one that is right for you.
Yes you could play a no skill ganker and have a fun time but in the long run noobs playing these characters will lose more games and let the team down more then noobs playing support characters.
Finally i would suggest you realise what took me afar too long to realise, if you want your stats to be good in the end, while you practice and get better at the game play characters that are not squishy's.. ie characters that are generally hard to kill you will rage less and generally end up with better games and stats.
I would suggest learning to play on Kepper of the Forest (personal favourite) or Accursed, both of these characters can be played for support and are hard to feed on, ie you will be a good praya and help your team win even if you are horrible at the game like i was for my first 150 or so games haha. (kinda still am now tbh)