The specific answer depends on the circumstances, but those who work with the homeless every day agree you generally should leave social services to the professionals.

"Most communities have some kind of crisis hot line, or the local United Way will have a 211 line," said Brian O'Malley, executive director of the Homeless Services Coalition of Greater Kansas City, in Missouri. In some cities, including New York, the hot line number is 311.

Your hot line call will prompt a local homeless services agency to dispatch outreach workers to help the person in need, said O'Malley and his counterparts in New York and Charlotte, North Carolina.

"We've been doing this work for a very long time, and what we tell people is it is better to donate funds and resources to organizations that are in the business of helping homeless people and have professionals on their staff who know how to do this," said Stephan Russo, executive director of Goddard Riverside Community Center, the lead homeless services agency in Manhattan.

"If you see someone who's clearly incapacitated, the best thing is just to call the police. The police know how to handle it," O'Malley said.

Still, there's room in the experts' doctrine to allow for direct acts of kindness.

"If you see someone who needs a coat and you have a coat, offer it to them. I don't have a problem with that," O'Malley said. "If the person is reluctant, lay the coat on the ground and leave."

"We don't really promote giving people cash money," said Deronda Metz, director of social services for the Salvation Army of Charlotte, North Carolina. "If you have a blanket, that would be great. If you have food to give, that would be double good. We don't promote giving people a ride."

Metz recommended that people who want to give direct help to homeless people do so in pairs for the safety of all involved.

Whatever you do, don't give someone alcohol, O'Malley said.

The advocates all agreed that the best route is to allow trained experts to provide services, but you can help people access those services.

Ask specific questions, O'Malley said: Do you need something? Can I get you a ride somewhere? Do you need food? Is there someone I can call for you?

Once you know what the person needs, you can make the call to the hot line or 911 and give helpful information, he said.

Many times, people won't want your help, said Christy Parque, executive director of Homeless Services United, a coalition of homeless service agencies in New York City.

"Sometimes people forget that [homeless] people have the right to ask for help or not ask for help, and it's tragic sometimes, but we need to respect their rights," she said.

Furthermore, your well-intentioned effort could be counterproductive, Metz said.

"The reality of it is that person may have a health condition and really need to get out of the cold," Metz said. "Your providing the blanket may not be a good solution. ... We've had incidents in Charlotte where people have frozen to death behind buildings, and they were covered in blankets."

Russo concurred.

"There are times when groups will come into the city, [trying to help folks,] whether through food or a blanket -- well-intentioned -- but we don't want it to be more comfortable for people to be there. The goal is to get people off the streets and into housing."

The best approach is to support -- through donations of coats, blankets, food, cash and time -- agencies that have the infrastructure and expertise to help the homeless effectively, the advocates said.

"Just giving somebody a dollar isn't going to help them from freezing to death or dealing with a lifetime of mental illness issues," Parque said.