Having never travelled anywhere even remotely like Marrakech before, the Medina was an enormous culture shock for me. It's nothing like anywhere I've ever been before and my initial impression was just 'madness.'
The medina is very busy at almost every hour of the day. It is crowded, noisy and smelly (sometimes good, sometimes bad!), there are bikes, motorbikes, taxis and donkeys pulling carts everywhere and not on any particular side of the road, so DO beware of traffic. As far as we saw, they won't crash into you - they know what they're doing - so don't stop/play chicken with them, just keep going and be aware of who's moving where around you.
Locals in the medina LOVE tourists. Tourists are where they make their money. If you need to look at a map, try and do so discreetly as you will be inundated with offers of guides if you show off that you are lost. DON'T go with a guide unless they have been arranged for you by your Riad. The street guides are pushy for money, and while most are harmless, are more likely to get you lost, taking you to small squares and shops where they can get commission rather than where you actually want to go. We made the mistake of using a guide, gave him 100 dirhams, and he harassed us for more quite unpleasantly - not a mistake we made again!
Women should dress respectably as the culture in old-city Marrakech still requires many women to wear full burkha and headscarf, so short skirts/shorts and low cut tops will draw unwanted attention to you. Also expect stares if you are blonde - things that make you different attract attention!
If you want to buy something, look around at a few places to get prices. When you have an idea of how much it is widely sold for, go for it. DO haggle. We found that most traders were not offended if we offered them half their initial price, and if you start to walk away, they will lower the price even more. NEVER offer more than you are willing to pay. And don't waste their time - don't start to haggle over something you're never going to buy.
The medina is beautifully rich with local food and crafts, and is a wonderful place to just walk around and take in the sights. While it can be intimidating to get the attention of every trader you walk past to begin with, they are (from my experience) harmless and are jsut trying to make a sale. Once you get used to where you should be going and work out how to navigate the medina, it's much less intimidating. If you ignore the shouts of traders and other overly-interested locals, they will more often not give up straight away - tourists are good for them and the last thing they want is to get a bad reputation for scaring them away.
After a couple of days, you will relax and feel more used to the medina. Then you can really enjoy it and take in the culture and sights.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.