As some of you know, I work in this sector (remotely, now, for a charity in the UK) and, quite frankly, if the answer were easy it would have been done by now. It's easy to pontificate from a nice house and a well paid job.
The causes of homelessness are rarely straightforward, but tend to revolve around poverty. Even substance misuse is only a real problem if you're poor, as any trust fund gakhead will show you.
The solutions are equally complicated. Homeless hostels are, by and large, horrible places, even the honest ones. Not all are honest; one hostel for women in Sunderland forced residents to work as prostitutes, as a report by the Tyneside Cyrenians in 2005 showed. I'm not naive enough to think anything much has changed.
Finally, an anecdote to think about from when I worked for a homelessness charity. Female addict lost her family because of her addiction, and had care needs that partly caused her addiction and partly stemmed from it. DAT wouldn't treat without the care needs being stabilised, social services wouldn't sort out the care needs till she was sober. Went on for months, back and forth, I couldn't get either side to budge. She killed herself. And yes, that news got to me.