I recommend reading Dakpo's analysis for some insight on how her moves work & when you should use them, and definitely watch the videos. I'd link it but i'm too much of a lurk to have the post count to do that right now. It's called "Zss just won both of the invitationals and here's how"
As for customs, I like Whip Lash, aka Side Special 3 more than the others. It's harder to use than her standard Sideb since only the tip of the whip does anything, but more rewarding because it puts your opponent in a position where you can possibly hit them with whatever aerial, UTilt, or USmash. Breverse & wavebouncing helps with spacing both that & lasers if you know how.
I typically try to hit people with a sideb3, UTilt out of shield, laser and/or DThrow which can be followed up by a few things while just plain putting you in an advantageous position, DSmash when expecting an air dodge, roll, or some other read, and try to get the most of out of juggling. Upb, FSmash, and Downb are her best kill moves.