Puff is a very difficult character to practice alone, honestly. Most of her mileage in a match against a human opponent comes from good reads, and understanding and counter-playing your opponents objectives. That being said, it's always important to have the best control of your own character as possible to maximize your ability to focus on your opponent, rather than focusing on yourself. The worst thing a puff player can do is get an opportunity, and drop it due to a tech error, since in higher level matches good opportunities are rare.
I would say just make sure you're comfortable with the ins and outs of the character. Consistent wavedashing and L-cancelling are both important basic level stuff. Against fox and falco, make sure you can up-throw rest consistently (use training mode to change their % to be higher or lower to practice different timing). Practice jab reset rest timing, aerial maneuvering and spacing, and just doing your best to make sure you're prepared to rest in any situation you can. Up-tilt, up-air, techs, throws, pound, just finds ways to link all of these moves into rest against different characters (prioritize higher tier characters). And then finally, work on your gimping/offstage game.
The problem with practicing puff alone is that computer always recover the same, making practicing gimping only so helpful. This is the same for rest setups, since coms won't tech randomly or DI most of your setups. That being said, it's still important to have a good understanding of the timing and execution for these things, so for a beginner all of these things are great to focus on
