How may I serve to benefit all other beings? By being completely present to the action of this moment. When the question is asked, the answer is created. If one feels frustrations when helping others, then one is not being present. Instead, one is likely thinking something like, "Others would be better served if the present was not like it is."
I hear folks claim not to have anything to share with others, yet I know from experience that we all have something to share with others. The bigger question is, why do you think you don't have something to share? The guilt comes from the knowledge that we have something to share but instead choose to spend our money (or resources) on something other than sharing. For instance, a one bedroom apartment can house 5 people or more; however, our privacy is more important to us than asking a homeless person to come stay with us. So, seeing a homeless person triggers within us the thought that, "I have a home. He does not. I could offer to share my space with him, but then I would have to give up something. I don't want to give up something so I will not offer." This consideration goes against our natural essence of brotherhood and love. Therefore we feel stress. So we make up stories to try to help ourselves feel better.
A recipe for happiness: Look within to find what makes you truly happy - continually do more of that. How to tell if what you are doing is making you truly happy -as opposed to a temporary happiness: think, if I did this to excess, would everyone concerned benefit? In this way, one knows that drugs doesn't make one truly happy. But smiling at the cashier, does. Giving food to someone who is hungry, does. Helping a homeless person find a home, does. Introducing another to the Dharma, does. Meditating, does. Drinking alcohol, doesn't.
It is my belief that everyone already knows how to become a Buddha. However, "Who wants to do THAT? I'd have to give up THIS." So we choose the "bliss" of ignorance and instead of "just doing it", we practice, hoping that we will grow strong enough to give ourselves up for the benefit of others...and that it'll be worth it!
As Yoda said, "No try. Do."
May these words be of benefit.