Riven is a champion that is cooldown based with and emphasis on timing and combos.

She is really fun to play as too.

Since all of her abilities are physical based and have realitivily short cooldowns as is I went with the standard Armor Pen Marks and Quints then Armor Seals and Magic Resist Glyphs.

Start with Doran's Blade. Move on to Wriggle's to assist with farming and for the survivability that comes with it. Next would be Mercury's Treads for pure survivability. Sheen is a good choice because it stacks with her passive. Next would be Avarice Blade to eventually be built into Ghostblade.

For Trinity Force if you don't want to wait and get it all at once then whether to get Phage or Zeal is dependent on need. If you team has snares then Zeal otherwise Phage. Then once you get Ghostblade she is kinda beast by this point. Bloodthirster and Infinity Edge is on here to make it where you can basically start facerolling people.

The first 3 levels are set in stone. 90% of the builds you see should start like that and the other 10% would start Q,W,W,E if they are going to max out the W ability first.

For this build I advise following the skill sequence to level 11 after that skill up based on what you need.