Hmm new to the league?
Well i've played a lot of this game i've gotten 3 accounts to level 30 and play a lot of ranked.
I would say the main things about a good game would be:
CS (this is vital early)
Learning all the roles efficiently
Countering an item build
Correct warding (yes its not just the supports job)
and Communication with your team.
As people have said before you really do need to focus on early game CS because if you don't last hit well, when you get to more competent players (i.e level 30's even though they aren't all the competent) they will overtake you in gold and a lot of the time XP. This will probably throw your lane so make sure you always have greater or atleast close to equal CS to your opponent 30 minions is atleast 600 gold which is enough to pull out an edge on you.
Learning all the roles efficiently this is one of the most useful things i probably did. The reason behind it isn't so you can fill in the unwanted position it's just so you know in game the play style of different positions so when someone comes to help there team or they swap lanes mid game (happens a lot at high level) you still have a good chance against that player.
Countering an item build, basicly you need to keep tabbing whenever you have spare time to just check what the enemy team is doing. so if you went against a laner that stacked 100% AP no armor or magic pen the first thing i would do would be to buy something with magic resist and spell ignorance (i.e banshee veil). Or if you know they have a lot of CC (crowd control (slows stuns etc)) buy something with either spell ignorance or something that dispells stuns and slows.. also you never know if your team is checking what they're building so if you notice they're all building AP instead of any AD then you need to take the time to tell the team this.
In my opinion wards are one of the most over powered items in the game. they don't just show player positions but they also show when they're attacking things like blue buff and gives you the perfect chance to steal such things. they show you when you're going to get ganked and if you have good team communication you can actually get your team to sneakily counter the gank by ganking them. Also it gives you an idea of how good the other teams map control is and hell it kind of gives you an idea about how much gold they have.
Finally there's team communication, if you want to have a good chance of winning you need to be nice and vocal with your team (not just ping random places with no explanation that's just damn annoying! for the whole team.)
try writing what you are pinging about. communication is key because there are 5 of you, the chances are you are going to see something that other members of the team missed out on.
Anyway i could go on for pages about tips for LoL (hell i have on some forums and my website and youtube videos) but i shall stop here
I wish you the best of luck, hope i have helped and i apologize if i had grammatical errors i am dyslexic!
