It took me a long ass time to really get comfortable with them and do them properly.
I flick a tad late. Front foot further back than for a kickflip. Back foot in middle of the board, maybe slightly over to toe side like a tre flip or bigspin, so that when you pop you can tilt the board towards the heelflip direction and your flicking foot will catch easier. I try really hard to flick down and keep my front knee from going too high, and aim for the side of the board instead of off the nose. And once you pop you want to shift your weight to be over your front foot as that is the fulcrum of the rest of the rotation. Might also help to scoop the board frontside a tad when you pop, maybe maybe not.
Learning kickflip noseslides really helped too haha.
Fucking show-off
(JK)
Can you hardflip
@sacking rails? If you can the motion of a FS Flip is very similar, just rotate your shoulders and lower torso and you'll be Muska-ing them in no time.
If you can't then back to the drawing board. Here are 3 things I focus on:
1) back foot - slight scoop of the tail, slight FS Shuv position to help the board rotation, too much and you'll end up with an Illusion flip
2) shoulders - parallel with the rails of the deck but you'll need to open them up and lead the rotation as you pop, that will help you get your body rotated and caught up with the deck underfoot
3) front foot - a little further behind your kickflip placement so it has space to slide up and rotate the FS 180, flick off the side of the nose just above where the nose kicks upwards (like
@tzhangdox said), definitely not straight off the nose like a kickflip, the flick of the toe is there to give enough of a nudge to get the flip, dont flick down unless you want a FS double flip
Similar to most 180 flip tricks, its about loading pressure at the right spots of your board and releasing the tension under your board at the right time. So experiment with a few front / back foot positions. Reynolds has his front foot way flat and covering most of the board (could be because he's riding a 7.75"), but compensates with his back foot in an exaggerated FS shove position.
Getting a solid scrape of your tail helps too, like he demonstrates at 0:19
Ben Degros has his front foot behind the bolts and back foot in a slight scooping position, so experiment with both front and back feet.
3:50 - scooping kickflip that you move you front foot out of the way and bring back to catch.