Chances are you're going to get feeders sometimes, you can't really do anything about that except avoid getting frustrated by it. If you focus more on improving your own gameplay and getting good enough to carry despite having heavy teammates then you will climb more easily.
You've got to learn how to better take advantage of rotations and openings the opponents give you. If your teammates are heavy (can't fight) the enemy and they are taking dragon, go to top side and push a turret. Try to take objectives that are across the map from the enemy so they can't stop you.
If one of your teammates is the fed one and you are having a hard or even just neutral game, it is important to group around your strong player so that your team will have the best chance of protecting them and getting carried until the weaker players can get caught up with items and XP.
Morale is a big deal too, teammates will perform a lot better if they feel supported and respected by you. Encourage them when they do well, console them after they lose a skirmish or get ganked. This does wonders for me to keep my teammates from tilting.
I recommend watching various youtubers that discuss strategies and frameworks to help strategize and gain advantages even in small ways throughout the game. Some examples who I've learned useful tricks from include Stonewall008, Gaming Curios, Phylol, Midbeast, etc.