The absolute best thing you can do for Skin the Gerbil is to keep the entire trick moving in one fluid motion. You could have your gap shimmed out the size of the grand canyon and it’ll still die if you keep stalling in between steps just because of all the string piles. That and make it as straight as possible.
The main pinch in Jade Whip is really made between your thumb and index, but like YoYoBob, I like to use my entire hand, and get the aim down by trial and error. Also like him, I never really keep a specific aim in mind, and just guide the string into the slack with a straight-down wrist twisting movement. It also helps to keep the motion forceful. It will “find” the gap better than it would for a wimpy whip.
It may help on Gyro Flop to just do a regular plastic whip and then just grab the back string and pull it forward. If you do it the way Andre does it in his tuts, it helps to pop it up and whip it in one motion just like a regular Plastic Whip, and instead of pinching the string with your non-throwhand, just have it loosely on there as a guide.
And most importantly, keep practicing! Skin the Gerbil and Jade Whip took me months of revisiting before I had them down comfortably, but now they’re two of my favorite tricks to throw into a play session.