Depends on what they were trying to spy on, what their mission was. Sometimes they given token jobs at their countries embassy like a cultural attaché or activities director. They would settle in, build up a routine and establish legitimate contacts in the community. Then they would build up their resources, get orders from he and use their now established network to gather intelligence on what ever they wanted. Some missions were easier then others. Sometimes they posed as exchange students or radicals in another country and did similar techniques to gather intel.