General AD Carry Runes

Marks:

Greater Mark of Attack Damage (+0.95 attack damage) will make last hitting much easier. As an AD carry, it is your duty to farm up for the late game where your team will be relying on you to have your items and deal high DPS to the enemy team. In addition to last hitting, a lot of AD carries have abilities that scale off of attack damage as well. Running AD marks will help your auto attack harass and some abilities so you can have more favorable exchanges.

An alternative that some people like to run for marks are armor penetration runes. Certain champions like Graves or possibly Draven who deal huge amounts of physical damage early on may run armor penetration in order to catch their opponents off guard at how hard they hit. However, I feel that the difference early game is very small and would rather take the flat AD in order to scale my abilities and secure last hits easier.

Seals:

Greater Seal of Armor (+1.41 armor) is the most efficient rune option for this slot since it grants the most amount of armor possible out of the three slots. Having armor early game will help against auto attack harass from both the opposing enemy laners as well as minion damage which can add up to a lot of damage. The extra 13 armor you gain will also help mitigate early burst from some AD carries like Graves.

Glyphs:

Greater Glyph of Magic Resist (+1.34 magic resist) is the most efficient rune option if you want magic resist. Generally as an AD, you won't be building any defenses early on so defensive runes will help mitigate a bit of damage until your team builds aura items or you complete the majority of your core build. Magic resistance runes are very useful especially in lane since the enemy support or AD may have abilities that deal heavy magic damage (Tristana, Corki, Sona, and Lulu). Running magic resist glyphs will also help out in the mid game in team fights since AP carries will generally have a good amount of magic penetration. The magic resist glyphs will help prevent them from dealing "true damage" to you with their abilities.

Scaling magic resist glyphs are also another option for this rune slot. I would recommend running it if facing a heavy physical damage AD carry and a low harass or melee support.

Quintessences:

Two Greater Quintessences of Life Steal (+2.0% Life Steal), and One Greater Quintessence of Attack Damage (+2.25 Attack Damage). With Doran's Blade being a common starting item for AD carries, running life steal quints in addition to the flat 5HP on-hit heal from Doran's Blade will give you a lot of sustain in the lane. The life steal quints also scale very well as the game goes on which often allows me to skip the vampiric scepter and finish my other items quicker (Infinity Edge, Zeal, or Last Whisperer). The one AD quint is there to help with early last hitting under the turret which is a bit harder when you don't have as much attack damage.

While there are a couple of other popular rune set ups, I feel that after much experimentation, that this is the most optimal set up currently. The rune set up overall very well rounded which is great for blind pick games. Thanks for reading and stay tuned for more content in the future!