First off, you don't go to 798 to get a picture drawn. Only really clueless tourists get that done, similar to the clueless tourists who get ripped off at Montmartre in Paris. Best places to visit in 798 are UCCA, Pace, Galleria Continua etc. I recommend entering from the south entrance, walking up that street (visiting UCCA along the way), then making a left at the first major crossroad taking in the galleries along there, crossing the big street that runs perpendicular and then making a left to Pace. From there, continue to explore the side streets as you please and if you get tired go to one of the many cafes to recharge your batteries.