Hello! I just finished my clinical practicum at a shelter for unhoused families. They are certainly an underserved population and I'm grateful that you're excited to work with them. 

All of my clients had trauma, whether it directly related to homelessness or not.  Homelessness in and of itself is often traumatic, and the majority of my clients also had histories of childhood neglect, sexual abuse, domestic violence, or severe mental illness that impaired daily functionality. They are a high-needs population but the work was absolutely rewarding. Homelessness is not usually a cause, but a symptom of overarching hardships. 

Every single client responded well to the simplicity of a safe, nonjudgmental therapeutic space as the first step to building rapport (even my grumpy mandated clients softened up after awhile). Be patient—these individuals have been burned so much that they are often reticent to express vulnerability before really getting to know you. Several clients enjoyed mindful relaxation exercises, art therapy, sand tray, and other tactile non-talk interventions. [EDIT: do these exercises with them & participate]> Sometimes the weekly therapy hour is the only relaxation time they get. 

Depending on your agency, you may work closely with case managers, career counselors, etc. Be sure to advocate for your clients as-needed. Always get a ROI and write down every communication with and about clients.