Right now, Graves is extremely good because Lucian, Corki and Tristana got like 100000000000 nerfs. Basically, Lucian had a mid game power spike and was bursty like Graves. Lucian did everything Graves did but better, so now that he got nerfed to the ground Graves is usually a better pick. Graves' 2-3 item spike is extremely powerful with Infinity Edge, Phantom Dancer (especially with the Stattik Shiv nerf and PD buff, since Stattik was considered a PD but better until recent changes) and Bloodthirster (ultra lifesteal)/ Last Whisperer (armor penetration for da tanks). Attack speed is especially crucial to Graves because his dash increases his attack speed by a percentage and lowers the cooldown of the skill on every auto attack This means that the more attack speed, the more steroids and dashes you'll get. He does fall a bit off late game, but still does a significant amount of damage.
Mobafire guides are strictly for getting item build paths. If you want some real lessons, watch an LCS player (professional player) on Twitch or watch some LCS games on Youtube. Or, sign up for
http://www.skill-capped.com, but it has a monthly subscription fee. However, nothing beats hands on experience.