I was in Morocco about 30 years ago. Not sure if my advice would still be valid, but FWIW, here it is. All this is IME:
Visit the casbah, or souk. Haggle, as has been said. Make sure you have exactly what you bargain the vendor down to–you don’t want to talk him down to a figure, only to give him a large-denomination bill and ask for change. His reaction will be, “Well, if they had this in the first place, why didn’t they just haggle to this amount?” BTW, cash is king in the souk; credit cards are accepted by some vendors, but everybody will accept cash. Western hard currencies are welcomed, but local currency is fine too; I used US dollars, Canadian dollars, and Spanish pesetas, in addition to Moroccan dirhams, when I was there. All were happily accepted.
Avoid buying a drink from the water-sellers carrying tanks on their backs. Their water is questionable, and there are very few public washrooms available. They are colorful and cultural, though, and will gladly pose for a photo in exchange for a tip.
Respect the cultures and traditions of Morocco, and Moroccans. You will see people in Western business wear on the streets, as well as men in traditional djellabas, and women scarved and veiled according to Islamic tradition. Like the former, the latter are going about their normal business, and don’t want to be bothered by tourists looking for photos, or commenting on them. For them, this is an everyday affair. Your tour group may have arranged some traditional Moroccan events at which you can take plenty of photos. Still, no harm in listening for the muezzin to call the faithful to prayer at noon, or in taking photos of some particularly beautiful mosaic work on a mosque.
You may be bothered by children, looking to act as your guides in the cities. They’re trying to make some money. They don’t take no for an answer, and they will follow you, but insist they are “guiding” you. Best thing to do is know where you’re going so you don’t need to ask for directions, but also to have a good supply of small change handy–they will claim “you owe me for guiding” when you get where you’re going, but they can be appeased with some coins.
Good souvenirs include brass work, leather work, and textiles. I still have a beautiful, hand-woven blanket I bought in Morocco, and a nice hand-worked brass tray.
Expect to pay a lot for alcohol. There is no prohibition on alcohol for non-Muslims, but Morocco is a Muslim country popular with Western tourists. So, they will supply it–but at a price. As an example, when I was there, a bottle of beer in a bar was about three times what I paid back home for the same thing.
As always, politeness and a willingness to communicate goes a long way. Although Arabic is the official language, French is widely understood as a result of history, and many people understand English. Naturally, in the name of politeness, you don’t want to insist that the Moroccans use English, but IME, they didn’t seem to mind if I tried English first. If my native English didn’t work, I had no problems with using French. I don’t know if you speak Arabic or French, but since French may be more familiar and easier for you than a crash-course in Arabic, you may want to bone up on bonjour, s’il vous plait, merci, and other polite and common French words and terms that help with communication.
As I said, it’s been 30 years since I was there, but I hope this is helpful.