Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Those masteries are pretty important. Move speed is important for staying out of range and keeping yourself alive from any number of things. Attack damage because she is mainly an auto attacker but her ultimate needs a lot of damage to be useful.
Ghost is mainly for escape. Not much else to say.
Exhaust for slowing them down or weakening a killer nuke.
Other Good Spells
Clairvoyance: seeing you target for your ult
Flash: instead of Ghost (she kinda has a wall jumper already)
Ignite: lower their healing rate and Regen while they running so your ult can finish them
Teleport: for those who have wards and want the perfect angle for that ult
Those Items are the most important part of this build. She is the type of character who does more damage the faster she attacks. He passive works great with Madred's and Black Cleaver. And the Bloodthirster's work great to add a lot of damage to her ult. They can be switched with Infinity edge if your worried about dieing to much but if your staying behind you team like you should be you'll be fine.
Runes are more of a personal preference area. Those are just the runes I have and I do well with Cait.