Have lots of tea, try tagine at street posts, be ready for pushy sellers, to haggle if you want to buy anything, and to be told by sellers that everything you wear and eat anywhere else in the world is processed petroleum from China.
(Don't be fooled, it's all lies, prices for tourists are gouged to hell, I bought the belt I'm wearing right now for 15 euro when the guy was asking for 35, and he surely made a good profit)
Considering doing a one-day excursion to Essaouira, a seaside city, which also provides sightseeing of the countryside. The driver will make you stop at a café, then an argan oil cooperative, and probably some bizarre sight. (Ours stopped at a tree on top of which some dudes had placed a bunch of goats, and charged for the sight)
I also recommend an excursion to the Atlas mountains, for instance to Ourika Valley, it's quite an experience and a beautiful sight, and the (insane amount of) tourists are mostly Moroccans so everything is much more authentic. Don't trust the driver's recommendation for restaurants if you go, or you'll eat overpriced shit that gives you terrible diarrhea.
Maybe plan a third excursion, 4 days are enougj for Marrakech IMO.
And enjoy, the place is beautiful. Just beware there is a whole sector of the economy dedicated to scamming tourists, but evading them is part of the fun.
PS: If you want help, don't ask idle men nor kids. Ignore them. Ask women exclusively, especially if they are in the way to work, or with the kids, or whatever. Otherwise, have a tea and then ask the café owner. Otherwise you'll be strolled around for an hour and end up at some shop.
PSS: Marrakech is poorer than other cities (Essaouira is even poorer, the countryside is just dire) and people don't like to feel like animals in a zoo. Careful with the photographs. That, and the idea that you ask permission then pay for someone's photo is very ingrained. Same with shops. People in Fez mocked this whole thing, but in Marrakech it can get violent and offensive for everyone. Try to be stealthy and polite, and if someone gets offended just delete the photo. You are entering a place with a different prevailing mindset, so even though it sucks one has to accept it. My advice is if you want to photograph people you integrate them in the environment and pretend you are photographing the environment around you. That, or just have money readily available, but some people will expect good dough and get even more offended otherwise. Just not worth to get everyone including yourself angry IMO.
PSSS I'm focusing in beware this, beware that... Because it's all everyone does when talking Morocco. It's great and very safe, this is just petpeeving. Enjoy your stay, it's great fun and you'll meet many nice people.