Riven is definitely an overall BAD ***, but she can be pretty difficult. If you're gonna play her get to know her skills. For one, her passive gets ignored quite a bit by players new to her. Her passive which adds increased attack damage after using an ability adds a ton of damage, damage that helps win most fights. A good combo to use when fighting, at least when initiating, is first initiating with your "e" and then auto attack. After, use "q" another auto attack and then "w" and an auto attack. Finish with "q", auto attack, and "q' once more, along with a final auto attack. When using Riven's final "q" try to aim it in front your enemy so they're knocked back and not away from you. A full Riven burst is slower, but deals more damage than most. You won't be able to kill a target with a single burst so be careful.

When laning be sure not to get too aggresive, however bursting the enemy every once in a while is great; especially in the beginning. Warding is a definite! You may not die when you get ganked but you will have taken a good chunk of damage from it, making it impossible to stay in lane. Always, always, always ward. To make riven especially effective, solo the top lane. Riven is extremely dangerous when just fed by minions. Don't get too impatient when you're getting no ganks or aren't able to get a kill; just continue killing minions. Not getting any ganks or not getting any successful ganks could be because of you. Allow your lane to be pushed a little. It makes ganking a whole lot easier.

Start "Red" when jungling. You're an AD character and "Red" is the best for her. After "Red" go wraiths and then try for a gank at mid or top. Continue jungling at wolves then back to wraiths and up to golems. If you have enough health left try for another gank on top or mid; if not, give mid "Blue" and go back to base. Continue a normal jungle through out the game and gank as often as possible.
P.S. Flash can be used to initiate battle, but try not to.