When you come upon a venue look for the location where there is plenty of foot traffic in the public area instead of standing in a place that interferes with the operation of the venue.
These places are at almost every venue because the developers of the venue have created a path for fans to walk to the stadium.
Public areas are typically identified as sidewalks or streets closed off for the fans to walk.
Avoid setting up near where tickets are taken or police are working. These two items, the business of the venue and the security of its patrons, are what you want to completely avoid.
In the public place you are granted much more liberty by the authorities and you are demonstrating respect for them and their work.
Finally, in these locations, fans are not yet focused on getting into the stadium and are thus able to receive the Word and respond.