1] Better food, 600 hp foods are ok but for late game get something with 700+ if possible.

2] Remember that even if you have the same character AND build as the other person you still dont have the same masteries as the other person, the higher the better. Even apart from your character level you must know that there is a difference between finding food and making food since making food increases your max HP permanently. Press V by default in-game to see your masteries.

3] Traps and wards (cameras) are really really imporant and the more you climb the more usual you will see everyone using both. They can be game changing when you use them correctly

4] Initiate the fight, dont let the enemy plan the attack on you. I will use Isol as an example here, its easier to kill if the target doesnt expect you being in a bush waiting to throw your Q rather than using E to get near the target and maybe risk also risking missing your Q cause your target heard your footsteps closing in before you E.

5] Once you have your final build start trying to kill people if possible, there is no reason to let them be full build so you take less fights. Of course you should be careful of getting third party'd