I read in the Zohar that each time we do a positive action, the energy of that action changes our very nature. This means that each time we extend ourselves to do something that is contrary to our negative nature (our Ego), we create another positive spark inside us.
In reality, none of us do things for others; we do things totally for ourselves.
The only one who truly benefits from your positive actions is you, but through that change, you can grow and give that positive energy to those around you, those you love, those you want to share with.