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.
To initiate, W, Q, then E whenever possible. Follow with W again if the enemy still stands.
Malsdy is there to add -resistance to your AP spells, and then your Sheen will shine through and give you the bonus damage you need. With the mix of AP and strong AD with armor pen, you shell out some serious damage. Turning your initiation into a nuke.
Also, stacking more AS is pointless. With your Guinsoo's, Sheen, and Runes you hit the 2.5 cap every time. Life/Spell steal is only added late game, no point wasting early gold on it as you will need to save your money for more damage items.