This game's about 50% mechanics and 50% strategy. "Gitting gud" pretty much boils down to 3 things. You probably won't read it anyway but here's a very condensed version
Laning - CSing well, knowing how your champion and the enemy champion works so you know when to play safe and when to be aggressive, paying attention to where the enemy jungler is, using your abilities + mana better than the enemy, knowing when to back so you don't miss creeps. Comes with experience
Teamfights - pretty much just dodge abilities, hit yours, position well. If you are a tank, block abilities for your carries and learn when to go INTO the enemy team to lock them down, or stay WITH your team to protect them.
Macro-game - moving around the map smarter and faster than the enemy team, warding up, getting picks, understanding split push and Baron conditions. This shit will take a few months to truly understand
If you are a jungler, it comes down to learning how to clear properly + looking at the map and seeing what weaknesses you can exploit at any given time. For example, ganking a pushed up lane, or taking dragon when their jungler is top etc.
Or tl;dr just play a broken champion and roll your face on the keyboard.