Rabbi Elazar of Bartota said: Give to Him of that which is His, for you and whatever is yours are His. And so did David say, "For all things are from You, and from Your own have we given You."Pirkei Avot 3:7
Do not begrudge giving charity, since you are not giving away your own possessions but rather those of G-d. And give humbly, since the fact that you own money to give away--and that you have the free choice to do so--are your powers granted to you by G-d.
The Mishnah does not only speak of giving money, it speaks of giving of yourself, as well. Realize that your entire existence is dependent upon G-d-that you and your entire reality would be nonexistent without Him. You will then be more willing to sacrifice your own comforts and desires for the sake of G-dly ideals. Recognize that all you possess--wealth, strength, wisdom, artistic talents, etc.--are a gift from G-d and that it is only proper that you use them to serve G-d.
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Rabbi Yosef Yitzchak of Lubavitch used to say: When you make a decision to give charity and to help another person generously--even if your decision does not reflect your available means--new channels are created on High to produce all that is needed for the fulfillment of your good resolution.
--From Kehot's
Pirkei Avot
Holtzberg Memorial Edition