There are tons of real research on this. Just do a literature search through psych, business and marketing journals on "charity" or "giving". The amount and vagueness of the question makes answering very difficult, as there's no way to condense the whole body of literature into a single, short OnStartUp answer.
Here are top-level observations I always keep in mind:
- People are more willing to help if the smaller the suggested donation.
- People are more willing to help a single individual than many individuals, hence the usual appeal to help "Estephan, age 7, in Paraguay", instead of the "The Poor in Paraguay", complete with a pic and certificate of Estephan.
- People are more willing to help if they are (or feel they are) the only one who can help, a.k.a. "Bystander effect".
- People are more willing to help if they believe their help will be noticeable, a.k.a. "Futility thinking".
- People are more willing to help if other people talk about what they give, a.k.a. good old "Peer pressure".
- People are more willing to help if you actually ask for time, rather than money. (I think it was Journal of Consumer Research)
- People who've helped are more willing to help.
- People who are "happy" are more willing to help. (Thoits & Hewitt)
That's just touching on the tip of the iceberg. One of the more populist writers is Robert. B. Cialdini.