We took a Sunday morning tour of the market in Jerusalem in April. Our guide was Joel Haber ( funJoel Israeli tours, google him and read his reviews here on TA) he showed us visitors and tlv locals a vibrant wonderful market, told great stories and introduced us to foods we might not of tried otherwise...we all had the best time with Joel !
If you are a foodie a guide can enhance your tour. Take it Monday-Friday as Saturday the markets are closed and Sunday not everything is open since there is no fresh produce after the Sabbath(Saturday).
Joel is good. Another great guide for a culinary tour is, Debra Nussbaum Stepen.
If you don't want a full tour with a guide, consider getting a "bite card" --explained on website. I was hanging out at my friend's son's restaurant and a group with bite cards came by. They got their sample food and sample beer and seemed to be having a great time using the card.
I second (third) Joel Haber. I do know him in real life - and he is hugely knowledgeable about the Mahane Yehuda market in Jerusalem and gives great recommendations as well as being a real foodie who knows where to find the best.
He has also made a huge amount of information about the market available online:
The bites card is a nice concept but I'd say not necessary in order to enjoy tastes in the shuk: you can equally well go around and sample what takes your fancy. If you go to the Jerusalem forum, in the Top Questions you'll find some suggestions for Mahane Yehuda market.