Riven is a champion that is very enjoyable to play, she is very fun and very powerful if played well.
Riven is a champion that can easily be countered if you don't pay attention to the game, she requires a great skill timing and knowing when you can kill your opponent and when not so watch out what you do and FOCUS on the game. Focusing on the game also is a very important thing if you want to climb.

These are the masteries I always use when playing Riven, as a Riven player I'm really aggressive and so should every Riven be, if you use this page you can go aggressive, if you go 16-14 you can go more defensive in early and bum them once you're 6. They shall fear the power of the Blade.

Those are the runes I use when I play against champions I can beat even on 1v1's before 6. 9x AD Marks, 9x Armor Seals, 9x CDR Glyphs and 3x AD Quints.
Those as I stated previously are great to play when you play against champions that you can trade/1vs1 on early game, before you hit 6.
Those are the runes I use when I play against Malphite/Nasus/Renekton, these champions are kinda unbeatable before 6, you have to play passive as a Riven till 6. If you want you can take the previous runepage against Nasus, but if you get the CDR runes, he is gonna wreck you at level 7-8, so I recommend the Armor Pen page.I use 9X ARPEN seals and 3X ARPEN quints, 9xCDR glyphs and 9x ARPEN marks.

Cons: Riven is a really squishy champion, apart from her gap-closers she is a piece of cake in early game before she makes it to 6, mostly after the nerf to her Q she becomes a piece of cake since she can't do trades like she used to do before the nerf, so you should be careful what you do beforeYOU ARE 6.

Pros: Riven is a champion that can hyper carry in late game, since she has a huge damage that can be dealt to the carries, she can engage with flash E W and just p00p on their carries, however if she has a support that can defend her with her glacial power! huehue.