It's really important to use the right words to reflect your mission and your goals. It's also essential to be very clear. Since I'm doing two things, raising awareness for the cause by making cranes and trying to get people to donate to the JustOneCrane campaign, I have to make that very apparent when I'm writing the blurb for the Facebook page.
You want people to get involved because they care, and not feel like they are forced to join so be sure to phrase your sentences carefully.
Figure out an amount that you want to raise (be realistic now), and state that clearly. It's good to set an amount so that people have a better idea of how much to contribute. Then state the amount you want to raise with the information about your cause.