Down tilt into FSmash-Up has been working pretty well for me. When guarding the ledge, if you're at the right spacing, as your opponent tries to grab the ledge you can down tilt into regular FSmash for an early kill.

Up tilt x2 into up B gets a bit of damage off.

Dash cancelling now allows you to get up in your opponent easier and start attacking right away. Dash cancel --> up smash has been working well for me.

Neutral b can now change direction and be shield cancelled, so it can be used for mind games and bait.

A change from Smash 4 is that Little Mac's side b off a stage doesn't leave you helpless anymore so you can use it more freely.

Another thing is just to read your opponent's and time a smash attack. Being patient is always good because Little Mac is good at punishing opponent's mistakes.

Anyways this is just some stuff I observed during my couple days of playing Ultimate and 4 years of Little Mac on SSB4. Who knows, I could be completely wrong haha but I hope this helps!