On the note of SH rising Nair OoS, here are two methods (Many people have trouble moving the thumb quickly from X to A and with good reason).
Method #1.
While in the air, Z actually works like A, meaning if youe holding forward and press Z in the air you will do a Fair. You can have your index finger resting on Z while shielding and press it asap after SH OoS.
Method #2.
So what alot of newcomers don't know, is that you can use the C-Stick for many things other that Aerials and Smash Attacks*. One of those things is Full Jumping or Short Hopping Out of Shield, by flicking it Up. Try it!
By flicking the C-Stick up, moving your thumb further off the stick and on to the A button in one motion secures a tight Rising Nair OoS for me.
*another use of the C-Stick is to use it for letting go of the ledge without ever fast falling or moving away from the ledge, by simply flicking it "away" from the ledge.