1. Give them homes (e.g., homeless shelters)
2. Enforce vagrancy/public nuisance laws
3. Prosecute repeat offenders
Any questions?
Not much can done to reduce the number. However, a lot can be done to make them less a nuisance and relieve some of their problems.
There are two types of homelessness, chronic (experience homelessness for over a year) and temporary. Temporary homelessness is hard to define because they are often doubling up with friends and relatives, sleeping on porches, in garages, on sofas, in motor vehicles, and occasionally on the streets.
Only 24% of the homeless are chronically homeless. About 75% of the chronic homeless can not keep any type of full time employment due to mental or physical illness, disability, or long term use of drugs or alcohol. They do get temporary jobs such day labor. About 20% get some kind of assistance from family. However, most of them either have no family or are estranged from them. IMHO, the best you can do is give them some place to live so they have a permanent address and are not living on sidewalks, parks, and doorways, then attempt to get them work that they can do.
The temporary homelessness usually requires help getting a job, childcare, low cost housing, and food. People that are temporary homeless typically find a home, get some work, and are ok for some period, then some event occurs such as lost of job or eviction and then they are out looking for a place to live.