Earn a great CS score. The more creeps (minions) you slained the more gold and exp you will get. The mor Gold you will get, the more powerful you will be. This is easy.
Avoid free damage. Just avoid it, do not sure that you could land that skill, but the risk chances are high? Then do not evn try. You will hav your opportunity later in the game.
Know best champions for your playstyle. Look at the Meta Champions and decide what items or actions could easily counter them.
Know how to Snowball in LoL. If you see that your team lead, then you need to accumulate this advantage by further snowballing into their ranks. Never decrease the tempo, this is extremly important in LoL.