As soon as you arrive, many kids and young men will come to you offering their service as a guide. I'm not very fond of guides, but if you really want to find something in the old town you better go with a guide. They can also take you to specific shops, which are rather "hidden" for touristic standards.
I arranged one for 6 USD who would take me the followinh day to see all the madrassas, shrines, tombs, houses... We met early in the morning and he took me around in the morning. Showed me the famous houses, we visited some kind of private houses typically harari, saw a few artists shops... I payed him 3USD, and arranged to meet him after lunch. But after lunch he never appeared back so I went wandering around the old town in the afternoon.
I tried to find again the places we had seen in the morning (I had even taken notes on their locations) but it was impossible, all the alleys seemed the same, all the gates similar, all the courtyards identical!!