DI Down from marth's f throw -_-, you make f air spam sound safe, jiggz players wont get good if they depend on f air to pressure falcon at high %
I suggest mixing things like hitting one side of the shield then hitting the other, or going high randomly then fast falling to f air, and if they jump into it you get a free WoP usually f air combo. also theres the dirty double aerial trick, =) skank the up air and easy combo/rest.
A shielding falcon can really just knee or up air out anytime and hit you, so make sure you space well.
Also if you know they grab too much just pull off some aerials, randomly crouch and maybe fake some lag = nice easy rest
Unlucky on ntsc you cant DI away from shiek's d throw so take the f air or u air like a man
I find shiek hard myself, i depend on some nice air battles against him due to jiggz has priority, but shiek's f air and b air are too fast -_-. Edgeguard is pretty simple though (advantage jiggz)
Needles..just work around them, duck them etc and if the shiek isnt a d smash ***** go for some crouch cancel or shield rests lol ;D Also n air to f smash, like on most chars but shiek gets *****.
Also advice try force onto platforms, its one of my favourite tricks, easy rest too =) can be done in several ways, one of the most obvious is using pound (i think king does it into the ground on pokemon stadium against falcon) up throw fox/falco onto platforms, mindgames.
Id easily say fox is the most horrible matchup for jiggz, you realise how slow jiggz is and fox's camping is ridiculous (not the lasers, just the approach is simple and abusing with n air and stupid combos). Up throw is overrated, the jiggz should either DI slightly to the side or upwards at high %.
Hence i hate this matchup, I use counterpicks now... its your choice though if you wanna work on this matchup =).