Riad Tizwa was excellent when we visited a few years ago – fantastic service and about the most chilled out meal I've ever eaten the evening we arrived up on the roof.
We spent most of the time we were there walking around the town – most stuff is well within walking distance. The Riad is about a 10 minute walk from the Djamaa el Fna (the main square), but most of the good stuff is spread out around the place anyway. As Keppoch says, the place is a rabbit warren, and all the better for that. Riad Tizwa is tucked well out of the way down a side street – it can be a bit daunting wandering down blind alleys like this at first, but I certainly never felt threatened while we were there.
I'd avoid most of the caffs on the Djamaa itself, and try a few of the places on TripAdvisor. Street food in general is excellent and everyone's very friendly. I found my slightly rubbish French was more than enough to get by, and my smattering of Arabic helped as well – learning a few key phrases of the latter does help.
The souks are great to walk around in, and the banter can be excellent fun. Do shop around and haggle like crazy, otherwise you will be regarded as something of an easy mark. Taking the p!ss a little or general leg pulling is also encouraged – although wait for them to make the first move – they've a very similar sense of humour to the UK, and it's a good way to haggle. That said, wait for them to make the first move before going beyond the straight faced haggle approach 😉
