choose wisely , i mean when there is a free champs rotation play with them and try those with 1v1 bot or your friend 1v1 if you feel it easy or good for ur gameplay style then buy it , but just hmmmmm...... buying a champ watching someone else playing it? its not a good idea , bcz every champs has pros n cons so , u know champs have mmmmmm..... abilities some of them got ad scaling ap scaling passives and so much stuff , i'd recommend u to select ur primary role first !
then play with free champ of that role and then if you feel it like you are driving your own car , then learn everything about it , mobafire is best , then if you would successful to learn the badsides and then you can overcome them no one can beat your team , bcz if you are the counter on ur lane , dont worry if you would know ur champ n the champ next to you , u wouldnt feed him ,
and later in team fight if your team has someone to stun someone to tank and a fed adc , none can beat u