my basic practice routine is typically:
practice missing fair by a set # of millimeters as i cross to close on the opponent.
do various full hop zoning patterns on the walking cpu for 10-20sec.
Practice all forms of leaving platform with peach.
practice different DJ swing baits i use, ensuring that my float heights are within 1cm of what i want to select when exiting the dodge.
pick random spots offstage, visualize the fox being there firefoxing run off throw the turnip, drop finish, etc.
combo my opponent vertically. practice turnip combos on the opponent while they are in the air. Practice rapid FC nairs low.
practice momentum shifts on floats while visualizing various zoning moves that i have to beat.
practice Shield movement, retreating floats out of shield.
practice dashdancing and moving while interspersing low floats and sh aerials. practice platform combos off upthrow at various percents.
I practice a lot of setups into various turnip snipe edgeguarding practice.
i'm sure there is more, but i'm so confident of a lot of the old stuff that I don't practice it. Honestly the hardest thing on the list is probably still hitting turnips when a fastfall is required and making sure float heights are exactly what they need to be off of a fastfall in a full/DJ. Honestly even a cm off from the selected height on a float is gamebreaking at higher level.
to me, the most annoying things in tourney are dying from burning my float on a DJ if i miss the DJ timing and having the opponent win an exchange even though my read was correct because the spacing/height of my float was wrong. and those are followed closely by misjudging the current amount of momentum i have, causing me to misspace.
The Cooldown: finally, switch to marth, practice fine dashdance control and more zoning stuff with fair, then switch to pikachu and practice cool gimp combos (never forget to walk it off, you don't want to pull a muscle)