I always like to think of this, whenever you want sheik to go anywhere, you want to think less of a hypotenuse or angled path:
.../
../
./
/
(yay, bad illustrations/examples)
because her horizontal aerial mobility is booty, and using more "right angles", or straight linear vectors:
<----->
usually getting into position on the ground first, and using that fast ground speed with quick stopping power,
∧
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then augment vertically with the jump with her good vertical air speed.
You can still get behind a lot of people on crossup, but it's usually a tight-knit distance (like sometimes you'll have to be closer to your opponent before jumping), if you make good pressure though, you can sometimes do some cool stuff with compensating by using her ground mobility instead. Pivot needles, RAR fair/nair (or just bair), pivot grab, or if you've got true pivots down, you can space jabs/ftilts on their shield after dashing behind them which puts you in a reeeeally nice position (I'm working on getting these consistent).
Usually I find it easier to just bait the opponent's reaction then go for a slip around/punish though.
cool stuff I've found though on the ledge, Sheik's ledge jump needles (and I guess ledge hop needles if you retreat at the right time) can hit the opponent without lagging up majorly from landing (you can usually land onstage or regrab the edge without having to use vanish/chain) to snap back on the ledge, nice sting if they're getting too cocky or close with ledge pressure. ledge hop -> AD is deceptively good, but not something you want to do every time (as with most of these). You can also ledge jump -> fair on their shield, which is safe unless they guess what you do afterwards usually (or are MK and have a dumb stuffer for whatever you do), and you can mix up the fair with AD/bair behind you when you come down.