Step 1: The Law of the Fast.
In the scriptures a day of fasting is limited by sunrise and sunset. For example, an early dinner would be eaten before sunset on Friday and then nothing would be eaten or drunk until after sunset on Saturday, when one would eat a late supper. Though ancient, this method is still a great way to fast. By starting your fast in the evening you avoid strong hunger pangs that usually occur after the first 5-6 hours.
Ideally, the money you save from not eating those two meals you donate to the hungry.
This truly is a painless effort that even children as young as eight years old may safely participate in. However, do not attempt to fast if pregnant or if you have certain parasitic ailments (consult your doctor).
You may also find other benefits to fasting. As you subdue your physical body and pray and meditate you may find it easier to receive spiritual promptings and knowledge. Most studies also show that moderate fasting such as this once-in-a-month method are actually beneficial to the body.
So hold off the grub, donate your saved dough, and benefit in multiple ways through the Law of the Fast.
Step 2: Take It Out First
When I fast, the money I donate is pulled out of my bank account before nearly everything else (except taxes). I do this way because I know that every month I'll fast, then I don't think about it anymore.
And I think that's probably the best way to give; by instinct, almost automatically.
Cheers, and good fasting!