So a lot of times I see people do jade whips or other types of whips and it seems like it’s in slow motion. I know this is done by pinching the strings but what are some tips?
Like you said, pinching the string is a must. Make sure your string tension is neutral because otherwise the loop you’re whipping into will twist closed mid-whip. Experiment with where you pinch the string to find a loop size that you’re comfortable with (e.g. I like to grab the string very close to the yoyo). Other than that, it’s like all other yoyo tricks: just practice, practice, practice.
Yuki
Try to get the Iron whip abd memorized it. Then apply that same motion into the Jade whip when you pinch it but make sure to whip the string sideway about 45 degree so the string will definetely hits the yoyo
I actually had this discussion about jade vs iron whip at the last yoyo meet. About half of us found iron whip easier while the other half found jade whip easier. So you’re right, it might be worthwhile to try learning iron whip first.
Yuki
I have tried iron whip but I have a hard time whipping fast enough after popping the yoyo into motion
Do it slowly at first , when your hand gets familiar with the motion and memorized it ,you could do it at breeze but Andre said even when you get it down , doing it fast sometimes the string won’t hit the yoyo
Just practice a bunch, and go slow; make everything one fluid motion, from creating the loop, to pinching/grabbing the string, to turning your hand over. I found that being jerky just made things more difficult and inconsistent.
Jade whip was much easier for me than iron whip. It took me learning jade whip before i could get my head around iron whip. I’m in that half I guess. 
As far as speed goes, I think in the case of these two tricks a bit slower is better. Watching the trick is the trick.
You can practice tricks like i do :
-Try to visualized it in your head and create somekind of 3D enviroments . Paste the tricks image into that 3D screen and then run it at super slow speed , carefully watch the tricks , memorized every bits of it , the details , the speed , the way the hand motion should be .
That’s what i applied 1st before i practicing it , understanding the motion 1st then begin developed it