It has a lot to do with mindset. I was (and still am) in a very similar position. I was climbing great at the beginning of the season all the way back to plat 1 where I left off and planning to make it to diamond. Since then I have gone on a massive loss streak to plat 5 and subsequently a massive win streak to make it back to where I am currently at plat 2.
When I was on my loss streak I felt that I couldn't do anything to influence the game, every game was just queing up to lose another. Then I narrowed my champ pool and started only playing the champs I truly loved and had fun with and that I knew from past experience that I could win lane and then single handedly solo carry games (darius and renekton).
This then led to my win streak back and during it it felt like I was invincible. The mind set that I was going to be able to win every game was amazing. My teams were full of people who knew what they were doing and rarely raged. Even if I lost a game it never felt like it had ended my win streak but merely put a quick pause and then we were back in full swing to win.
I would also add that having at least one friend in the first few games in the beginning in an important role like mid or jungle to just ease your mind about your team mates doing badly so you can just focus on winning lane and then game.
TL;DR Find some champs you love and you know you can carry with and start doing just that.