I don't think I can help you a lot with Riven itself but I think it's mostly the way you take the lane, and not quite the mechanics. Lane understanding, minion wave understanding and control is a whole science up toplane and it's crucial to succeed. Mechanics are irrelevant if you don't manage your lane properly and understand when to trade, how to farm up safely, how to put pressure, how to snowball, how to face a snowballing person, how, when and why shove, how, when and why freeze etc.
I say that because I know I can hold a lane with Riven despite being the most garbage mechanically player on her by a long run, but I still know very well how to face hard lanes.
First advice I'd give you is that the most important of all things in toplane is exp. You can miss minions and not care thaaaat much because the most important is not to fall behind in exp. That's why you optimally want the lane slowpushing towards you for you to freeze [have the enemy wave bigger than yours, but not in range of your tower], to snowball a matchup or to survive a hard matchup. If however you wanna put pressure more globally, you can hardshove (DONT DO IT HALFWAY THE GUY MIGHT GET A PERFECT FREEZE) and go into their jungle or roam mid.
Don't play aggressive for no reason.
Good trades are when:
- the guy goes for cs'ing a minion : he has to choose between trading or losing minions.
- the guy misspositions and you can do freedamage to him
All ins :
-you are winning matchup and you can beat him. Ideally you want to NOT PUSH if you want to snowball on him. By doing so, he misses CS.
You want to have it warded. Be careful of attitude changing. If the guy that played pussy the whole game suddenly goes aggressive, he's probably having backup.
-He's low.
Dive conditions :
-You are confident you can kill him even if you die too.
-He loses a huge wave of minions
If those conditions are there, a dive is EXCELLENT and i can't stress this enough. Because the guy loses a whole wave worth of exp which is insane for snowballing purposes.
, and I'm running into a few aggravating problems. She is fun and can do tons of damage, but I've noticed in the past week, that I consistently lose lane, lose trades and just fall behind. I'm currently mastery 6 with 72K points atm. I've had a few wins recently with her, but I'm still not satisfied with my personal score. So, if anyone is gracious enough, I would love someone to coach me in games, and even train me on how to become a decent 
