Well to answer;
ARAM: Aram matches you vs skill levels close to yours dependent on their abilities in the gamemode, if you've done good with ARAM you probably will get good players, however ARAM is inherently unfair and will usually be unbalanced due to the fact you can be all melee vs all max range mages. Not to say it is unwinnable but ARAM is unfair, accept that as fact.
SR Normals: Summoners rift normals works the same way, placing you in a skill group similar to your own, your AD, JUNG, MID, ETC feeding is due to them losing, do the same thing to their laner, don't make your own mistakes, try to carry, if you lose, oh well. Not much else to say, if you wanna win so badly just go on a tier list and pick whats OP, run Dark Harvest, win lane, try to win game, or stick out with a fun pick and just enjoy the game as a game. Your choice.
However, your last 20 games according to Na.op.gg 19 of your last 20 games are ARAM, and you won your last normal game, so honestly, stick to normal games really or try Nexus Blitz, theres an URF minigame, so its close to that. Its casual and honestly fair, plus you get to try old items like DFG, Force of Nature, ETC.