so you want to rank up?
step 1. admit what wins games. and thats inhibitors, barons, objectives, gold leads and team composition.
step 2. stop chasing kills, the reason why they are running away is because they want to live. and back. consider this, is the 300 gold you'll get for the kill more important than the 750 gold the tower they were defending is worth.
step 3. get good with a handful of champions, take them to bots if you have too in order to understand what your champion choice can do. play more and more games with them. understand what all the items you buy can do for you and how powerful it makes you feel when you buy key items.
step 4. use your flash defensively to evade things, not after its already happened to try and escape death.
alternatively use it to secure a late game kill. by flashing forwards to get some cc on a carry or finish someone off. 5v4s in the late game are big game changers.
step 5. rally your team together and go some place together, i guarantee the enemy team wont know how to react and you will have hard numbers advantage and will take objectives for free uncontested.
step 6. push when you have an advantageous lead, even if its a meager 2 or 3 kills lead. you are favored to continue winning and snowball. or just a back before the enemy laner, you have items and full hp, he doesn't.
step 7. go after whoever is the strongest/best on the enemy team, without that player their whole team will fall apart without their key player.
final notes.
i cant guarantee the victory every single time. but you have to start with getting a gold lead somewhere/somehow in the game. (most people have trouble with this, but you should aim for 80 cs every 10minutes at the minimum, its free gold you pass up on. to improve last hitting just start a solo custom game if you are serious about it.)
i will assure you that the majority of low ranking games are won when the first inhibitor is taken, i wont say comebacks aren't possible, but having an early inhib is such a strong indication who will win.
getting towers and then grouping is near impossible to contend with.
these aren't the only things a player should consider throughout the game, ofc i haven't touched on warding, meta, and timings powerspikes. but thats also for you to discover and find what works for yourself.
im only offering you here the core foundation and the cheesiest quick and dirty methods to win the match and assert yourself as the dominant player.
the majority of low ranking players dont know this.... but you do now. inhibitors and gold leads win games.
towers are worth WAY more gold than kills.
cs is free gold in your pocket.