Personal interactions have the strongest impact on perceptions. People form opinions of the police based on their own interactions with them or the experiences they hear from trusted friends and family. 
People tend to focus on how police treat them — the process and interactions — rather than the final outcome of those interactions. For example, research shows that people report positive impressions of an officer who treated them fairly and respectfully even if the officer gave them a speeding ticket. 
Research also shows that an officer's demeanor and actions are crucial to perceptions of police legitimacy. If officers communicate well, listen and treat citizens with respect, citizens will respond in kind. 
People who perceive that they received “procedural justice” are also likely to perceive the police as legitimate and trustworthy and are likely to comply in the future. Procedural justice is the notion that a process is fair and that people have the opportunity to be heard, are treated politely and respectfully, and are judged by a neutral system free of bias. 
Media accounts of police misconduct also influence perceptions of the police, but less so than personal interactions.
Frequent exposure to media reports of police abuse or corruption is a strong predictor of perceptions of misconduct and supports the belief that it is common.  African-Americans who live in high-crime areas and who regularly hear others talk about police misconduct are especially likely to believe misconduct is common.
Conversely, a nine-month study of five precincts in New York City found that in the absence of major scandals, news coverage of the police did not have a significant effect on citizens' views of the police. 
[note 1] Schuck, Amie, and Dennis P. Rosenbaum, “Global and Neighborhood Attitudes Toward the Police: Differentiation by Race, Ethnicity and Type of Contact,”Journal of Quantitative Criminology 21 (2005): 391–418. See also Weitzer, Ronald, and Steven A. Tuch, “Racially Biased Policing: Determinants of Citizen Perceptions,” Social Forces 83 (2005): 1009–1030.
[note 2] Tyler, Tom R., “Policing in Black and White: Ethnic Group Differences in Trust and Confidence in the Police,” Police Quarterly 8 (2005): 322–342.
[note 3] Horowitz, Jake, “Making Every Encounter Count: Building Trust and Confidence in the Police,” NIJ Journal 256 (January 2007): 8–11, NCJ 216524; Rosenbaum, Dennis P., Amie M. Schuck, Sandra K. Costello, Darnell F. Hawkins, and Marianne K. Ring, “Attitudes Toward the Police: The Effects of Direct and Vicarious Experience,” Police Quarterly 8 (2005): 343–365; Weitzer, Ronald, and Steven A. Tuch, “Determinants of Public Satisfaction With the Police,” Police Quarterly 8 (2005): 279–297.
[note 4] Tyler, Tom R., and Jeffrey Fagan, “Legitimacy and Cooperation: Why Do People Help Police Fight Crime in Their Communities?” Ohio State Journal of Criminal Law 6 (2008): 231–275.
[note 5] Weitzer, Ronald, and Steven A. Tuch, “Racially Biased Policing: Determinants of Citizen Perceptions,”Social Forces 83 (2005): 1009–1030.
[note 6] Miller, Joel, Robert C. Davis, Nicole J. Henderson, John Markovic, and Christopher Ortiz, “Measuring Influences on Public Opinion of the Police Using Time-Series Data: Results of a Pilot Study,” Police Quarterly 8 (2005): 394–401.