It takes time for a relationship based on trust to develop. Respect each person's boundaries and ways of relating. When you have developed rapport with a homeless individual, you can decide to what extent you want to and are able to help them. Explain to them that you would like to offer your assistance, but it is ultimately up to them. Your assistance may be as simple as offering to get them some clean clothes, or it may entail setting up a job interview for them.
Homeless people react differently to someone's help.
Sometimes a homeless person may respond defensively because they feel powerless, and may overreact to try to maintain some control over their situation by being angry and hostile before the other person could. Or they may have repressed their emotions so that when someone helps them, they just accept it numbly without showing appreciation. A homeless person just wants to be recognized, not ignored. Just making eye contact, smiling or saying hello makes such a difference. Acknowledging one's humanity is one small yet easy way to help the homeless.