The adc can't hit you if you burst them down first. I usually go all in on damage/mag.pen ... relying on my positioning and team to stay out of danger. If you think particular opponents are troublesome, build defensively accordingly, but not before youve finished 3 items. Honestly, in bronze, I would just build straight damage, it will help you snowball ahead, and youll be able to kill tanks. Later ELOs require some more strategic buys where you max/min damage/defense.
For example, I like to take velkoz, if the adc tries to duel me, I pop barrier and all in them with my combo. Unless they're way ahead, they don't stand a chance. Always know your opponents. If you're up against vayne, don't let her break your channel with her E, but that's understood, every game, be aware of what you need to do to outplay your opponent so you're not surprised... if you see an Ashe, be ready to side dodge if you see her getting too close (especially if her support is pushing up with her), since she's likely posturing up for an all in combo.
I see you like to play Ahri/Lux mid.
For Ahri, you should be able to kill the ADC from your combo. Use your R to close the gap then charm, then use your other skills Q/W, and other 2 Rs to skirt around them hitting killing them. The ADC should never stand a chance if you land your shots. Don't use your Q to run in, because you won't kill them and then you're vulnerable. W is only good for a few extra bits of damage. If you need to, land a few Q's from the edge, then when you think you can combo them, then go in with R.
Lux. Again, they shouldn't be able to get anywhere near you. If you miss your Q or E you're likely dead. Use E to zone, then Q once they are slowed. Or use Q to force them into E if they want to dodge. If you hit Q and E, then R them. Lux is relatively predictable with her strategy, so practicing so you're comfortable landing E right at max distance is what'll raise your skill cap. You may want to start taking comet, especially for lux since they can't dodge it when you hit them with your spells.