I guess ARAM may help with team fighting but I can't really think of how it helps with SR. Ranked is where similar ranked players come together to try and win games. Players are supposed to be playing their best roles and champions, where in ARAM champions are random and there are no roles. Besides pushing mid turrets you also don't have to worry about other objectives such as dragon or baron, a 1v1 or 2v2 laning phase, or worrying about split pushing/covering lanes.
If you want to get better at SR you need to play SR more. Figure out what 2 roles you like/feel confident in, find 2-3 champions you like in those roles and spam those roles & champions over and over again.