Although I'm no pro I'll give you my advice.
Looking at your match history you die alot with a score ranging from -3 to +3, so I'm going to assume you trade 1 for 1 alot. The thing is your champion pool consists of a lot of mid game champions; Zed, LeBlanc, Lucian and Graves come to mind. The problem with trading 1 for 1 with mid game champions is that a late game champion comes out ahead as they get closer to the late game faster.
Two, your warding and CS seems sub par. I would say that every you need to be getting at least 70 CS per 10 minutes. Also you should be buying wards on every back and always upgrade your trinket.
Three, there appear to be games in which you left for whatever reason. Never leave a game, as throws happen so easily. If these incidents are caused by connection issues then try to resolve them before continuing to play ranked.
Four, learn to support has a good support can win the game. Ward objectives peel for the carry. Mid game follow who ever is the most fed on your team and help them win the game
Hope this helps and good luck.