Hi, this is how I play Riven mid in ranked. I'm still working on this guide. I would suggest to tell your team to have an Ap top like Rumble, Singed, Cho Gath, Vladimir etc.. If u are trying this guide.
Because you will not deal any sort of Ap damage.
I only use build 1, but I would recommend build 2 if it's not going that well.

Well, to start of with Riven can just one shot most of the Ap carries, this is why I like Riven mid. You can get really fed and then just snowball every lane, and they will probaly not even focus you in teamfight's. Because of Riven's Q and E you can basically dodge most of the skillshot's from Ap carries. I wouldn't recommend playing Riven against a champion like Ryze, because he is fairly tanky and have zero skillshots and a bind. Zyra is someone I would recommend playing against because of her abilitys being very easy to dodge for Riven.

As Riven mid, the early game work's a little like this.
1. Help your jungler with wraith/wolves, tell someone else to pull red/blue because you can't
2.Farm until level 3, now you wanna go for the kill
3.Wait for the right moment to strike, when the enemy is very close to you jump in with your E and use W to stun ingite early and just spam Q.
4.If she/he died good, if not she/he probaly wasted a flash and you can free farm.
5.If you got a kill I would suggest that you push your lane and then b and get a dorans blade or long sword, now the killing begin's.

Glyph's

We need flat magic resist to be able to win the mid so it speaks for it self, but why a Ad glyph? Well, this is your choice either 16 Ad or 12 Magic resist, I prefer 16 Ad but it's your choice.

Mark's

Just some Ad to be powerfull in early game so you can go for that first blood.

Seal's

Armor is always good.

Quintessence

Some Ad to be even more powerfull.

Well 21-9-0 speaks for it self, we want a lot of Ad. This is just to get that early resist and a lot of damage out of masteries.