You want to farm while dealing damage to the enemy. Play very aggro and always trade them more than they can trade you. Once you get your ie you can always win trades and destroy them.

By this time you should already have 2-3 items. This means you can beat them in trades or just destroy the enemy without even trying. Keep in mind you are an ADC and this is the year 2017. That is why you need Mercurial Scimitar to make sure you stay alive.

By now you have a full build if the game even lasted this long. You are busted right now, all i have to say is go end the game and type GG. EZ