For airdodges, don't just spam them when you're in the air. Watch your opponent and wait until it looks like they are going to go in for an attack.
For spot dodges, try having someone do grabs or smash attacks and try learning the timing.
For shielding, try using your shield as a parry. Bring it up for as little time as possible to block a move and then attack. When holding it for longer when you are facing an aggressive set of attacks, mix up your out of shield option between jump, grab, and drop.
Also, "rolling is bad" is a good way to think about rolling. Not because it is always bad, but because most people roll by default and it usually is not the best option.