So I've pulled this off a few times in practice so some things to note.
At low % where you can link (chain) f-throw into d-air into grab, etc. This then extends onto the ledge. Allowing for a set up, or combo extender. Also if you think your too far away to reach the ledge in time for usable f-throw %'s, go for a d-tilt after the d-air to push them towards the ledge more then go for grab. And maybe you could trip anyways?
When is best time to cancel into rock? Sometimes I get a sweat ledge spike, other times they avoid it. Character dependent?
If you cancel into up special, make sure you hold back a bit, otherwise you'll SD...