Depends on what they're playing.
Mileena? Block low, full punish if lag isn't awful. Sub zero? Block low and repeat since almost all of them open with a slide.
Predator? Block the grab/laser, block the jump overhead, low bow swing out.
Scorpion? Block the teleport, punish.
Quan? For some reason they always open with a teleport in me and I found out by accident that Kung jin's dive kick will beat it in air, so I usually jump back vs Quan and dive kick. If it whiffs, can usually recover.
Kang? They're going for 4,4 and most can't cancel out into bk online so duck block wait for the flying kick to whiff, grab. Train them to be afraid of that 4,4 opener. If you eat a B2 instead that's a trade I'll take.
Kotal? Low bow swing.
Cassie/Sonya... Be afraid. If it's a dive kick spammer just wait. If it's someone who knows how to play her with actual combos, try to remember her strings cause I've got a lot of blocking coming up and sometimes with latency it doesn't even matter.
Jax? Usually they start with that superman punch, so block and then njp if possible.
Raiden? I usually block because it's either a babley or 1,1,whatever to start. You can tell the type of raiden player usually by this also. If they start with a superman, they're usually the type that loves to spam it recklessly, especially if they have meter on wake up.
Jin? Dash back, flying kick. Jin's love to start with that njp. And will often just sit there jumping with it repeatedly.
