I'm kind of betraying my main by posting this, but considering we are all people trying to learn from eachother, I'll help you out with some basic tips
- Little Mac is SUPER crappy in the air. If you can stay in the air as much as possible, it will be that much more difficult for Mac to land a hit.
- Try and be as unpredictable as possible. His attacks are fast and destructive so don't let Mac think you're going in for an attack otherwise he will just play defensive and once you use an attack he'll immediatly go on the offense.
- Remember that ZSS has a very long tether grab which doesnt need to be used at point blank range. Be unpredictable about it though. Don't spam it.
- Learn the Dthrow > Uair > Uair > Up-B combo. This combo puts your opponent in grave dange especially Mac because Mac's air game is so notorious he has no way to escape it other than DI (if the ZSS player lands the hits at a good angle and at decent timing). This move can also kill Mac very early considering he is a lightweigth character.
Other than that, I'd say just bait them to the ledge and then go for a grab in an attempt to throw them off then once they use their double jump, try and hit them with a Nair so they can't get back on. However, keep one thing in mind: smart Mac players always try to save their double jump as much as possible so dont lose your focus once you hit a Mac player away from the ledge as they try to get back on.