There are 2 key points for location;

1. traffic
2. ease of access

look for a spot that has very high traffic, either pedestrian or vehicle (if it is vehicle you must also have a place for people to park).

Church parking lots, bigbox retailers, gas stations are prime, but make sure you get permission. Depending on your product you have to consider overall area - industrial, residential or commercial.

Consider traffic times of day. Bigbox retailers will generally have there best traffic after regular business hours and weekends.

Church parking lots are usually good because they generally aren't needed much except for Sunday's and the odd evening.

Heavy traffic area but where it is difficult to stop gets you nothing unless you are considering a downtown area where people are walking. In that case it is best to be on a corner of 2 major streets intersecting.

Some gas stations like vendors because it draws traffic to their pumps. But if they have a store that sells food they won't want you.