Based on Chapter 5, "The Young and the Ruthless," in the textbook The Will to Kill: Making Sense of Senseless Murder, how can I use specific criteria from the lesson to explain a plan to reduce youth violence?

Chapter 5 explores the prevalence of youth homicides but also addresses the reasons for the decline in youth crime in the 1990s. The authors also connect juvenile crimes to the influence of drugs and gangs as well as the accessibility of guns. Interestingly, the authors raise the question of whether media-glorified violence is a contributing factor to homicidal tendencies among juveniles. Perhaps most importantly, the authors also provide examples of programs that are designed to combat and prevent juvenile violence.
From what I can see of the posted lesson above, William Bratton greatly stresses the importance of cooperative efforts between the mayor of New York City and the police department. Since Chapter 5 also stresses the importance of community efforts to combat juvenile crime (and the necessity of continuing vigilance in this area), your best approach would be to lay out a plan that incorporates these factors.
In fact, you may be interested in tailoring your plan according to how some of America's major cities (Chicago, Boston, Detroit, NYC) have come together to address the prevalence of juvenile homicides. To date, these cities have come up with a plan that focuses on four concept areas:
1) Prevention programming: This includes family and community-centered mentoring efforts as well as extracurricular activities for at-risk teens.
2) Intervention programming: This specifically addresses at-risk juveniles and youth who have already participated in gang-related activity. Intervention programming incorporates social services, health treatments, and educational activities.
3) Law Enforcement efforts: Police increase vigilance and efforts towards the most violent and serious cases of juvenile crime.
4) Re-entry programs: These programs help youth offenders after incarceration periods and are focused on education (high school and college) as well as job training.
Here's the link for the National Forum on Youth Violence Prevention's strategic planning efforts. Another link you might be interested in addresses how America's largest cities are utilizing coordinated and multi-sector approaches to combat juvenile homicides. One of these cities is Baltimore.
In 2014, the city of Baltimore worked with faith-based organizations, law enforcement, and interested community members to address the high rate of juvenile crimes in the city. The city introduced several important programs that are still in use today. Some of them are:
1) Emergency Room Violence Interruption Program: This program is a collaboration between medical professionals and the Baltimore City Health Department. It trains doctors to refer the youth they treat to appropriate city programs.
2) Youth Health and Wellness: This program focuses on the well-being of youth from the cradle to age 18. In your plan, you may consider emphasizing media violence (something the authors of the book do). For example, psychologists have concluded in recent years that media violence only affects teens who are already immersed in aggressive environments. Specifics of your plan can address how you will use community organizations and social programs to address domestic violence. For example, the city of Chicago has utilized cognitive behavioral therapy / social emotional learning initiatives to help young people develop social-emotional skills.
3) Baltimore Police Chaplaincy Program: This program incorporates the efforts of law enforcement and faith-based counselors/religious leaders.
4) United States Attorney's Office Project Safe Neighborhoods: You may be able to combine the above programs with one like this, where federal, state, and local officials work together to address the immediate consequences of gang-related gun crimes.
5) Youth Job Training Program, Mayor’s Office of Employment Development (MOED): You may decide to combine a program like this with one such as the Baltimore City Temporary Cash Assistance Employment and Training Program.
Based on the book and the criteria you reference, you're looking at designing a plan that incorporates community, federal, state, and law enforcement efforts to fight or reduce youth violence.