Well honestly GGXrd most advanced mechanics are the Roman cancels... which I'm not good at utilizing either. But really like most anime fighters its a matter of knowing your match ups and character's range.
Like with Sin and Ky their best tools is hands down their poking range. Especially with Slash it's really a good followup and a great way to get in certain scenarios. I usually go 6S,3S,3HS, Beak Driver, 3HS, into RTL.
Or with Voltic Dein I used as a great mix up or Aerial tool because that slow speed is more beneficial than you think.
With Ky on the other hand he plays mostly like XX Ky with AC+R tools. But most importantly he has far better projectile utility with his Dusts (Easily best Dust in the game), and Stun Edges. Me personally however if I want to make the most use of my damage output along with getting past Enemies burst, I'd start considering working on your Dust combos.
Elphelt on the other hand is a little tricky, she's not a good Dust character and with her it's mastering her frames and range which is harder with online lag.