Or, anyone with a PayPal button, for that matter.
Rule Zero: Make it simple.
This is a general rule for any time you are trying to get someone else to do something. In the case of non-profit donations, the donor is already giving you money, don't make it painful for them to do so.
#1: Explain the benefit.
Even if the donor is allowed to set their own donation amount, creating an itemized list of what certain dollar amounts can accomplish adds value to the donation, and encourages the size of gift you want.
#2: Try out some different calls to action
Sure, you just can use the plain-Jane "Donate" button if you want. It gets the job done, but falls a little flat just by itself. Phrases like "Give", "Lend a hand", "Create a scholarship", or "Snag a sweet tax write-off", can result in more clicks.
Only way to find out what works best for you it to try a few out yourself.
#3: Give your call to action the spotlight.
Donate some of your front page real estate to a cool graphic with a snazzy call to action, like this:
Link that to your landing page, and folks will have a much easier time figuring out how to give you money. Rule Zero, remember?