Advanced combos

So i have been playing riven for a while now, around 150k mastery and i have been doing great. I know the basics like fast q and doublecasting and q delay but i feel like that's just the beginning. Everyone talks about how riven is super combo heavy but i dont know any specific combos and usually just improvise with those mechanics. Are there any optimal combos that i should learn and which situations should i be using them in?