Surely if we cannot let go of material things, of mental things, of emotions such as anger, of other negative states or even of positive states, then when it comes time for it, we won't be able to let go of the self in meditation, to make that quantum leap to the unconditioned experience. Therefore the practice of giving is a whole and complete practice in itself. In your daily lives you can find many opportunities for practicing giving. There are three foundations of the Dhamma that help us as we practice giving. All those three work together.
Right understanding understands selfishness and miserliness as being negative states.
Having become mindful of selfishness and attachment as unwholesome states of mind, we use Right Effort to abandon them when they arise. Practicing Right Effort, we make the effort to prevent and abandon unwholesome states, the effort to cultivate and perfect wholesome states.