If you're an ADC main in League of Legends, you know the pain of trying to cs while getting bombarded by Xerath support. Sometimes you can rely on your support for help, but in soloq you can only trust yourself. Here are a few tips to help you.
The first thing that must be mentioned is that the game does not start after the loading screen, and once you are in the Rift. It starts in champion select and based on enemy bans you can infer what champions they are going to pick, with those bans usually being centered on hard engage champions, or champions like lulu. If you are later down the line of your team's pick, all the better.
You will want to pick champions that opt into Immortal Shieldbow as their mythic, with the Vampiric Scepter for sustain. Rush Berserker Greaves first to help you against enemy skill shots, and if possible, pick ADCs with dashes or a long-range on their auto-attacks and always start the game with a lot of potions. Remember, you win until the first back by using the starting potions to keep yourself as healthy as possible, and denying the enemy their kills.
As the mage support lane is heavily kill-reliant, it is never worth trading one for one due to the early scaling of mage champions and items, as well as their price compared to the items ADCs usually buy. Instead, auto cancel last hits on minions and sidestep to bait out spells, giving your support the opportunity to make a play, or perhaps even yourself if you see the chance, and are playing with enabler support, such as Zilean.
These tips are, very basic, and are intended to be as such. Any low elo ADC main can start applying them in the course of the next few games, and consistency in applying them will force the enemy mage support to fall off, and not give them the necessary gold to do what they do best, be annoying.