Should you be holding A down while getting ready for a jump then?
I haven't played a SSX properly before but its that classic Tony Hawk muscle memory kicking in.
Yes, this is called pre-loading in SSX. Pressing the stick/d-pad (depending on you control scheme) while you are pre-loading allows you to pre-wind your spin (means you can do a rotation or flip the instant you take off from the jump) for more trick complexity.
You'll know when you're pre-loading and are able to pre-wind because you won't be able to turn much at all.
The ubers are both triggers right?
Signature tricks (in Super Tricky state, when the TRICKY is fully orange) are performed by LT+RT+any trick button.