A bodhisattva is someone who has turned completely away from self-absorption and toward acting for the benefit of all beings.
So . . . to become a bodhisattva, simply let go of all self-concern and act with total concern for the well-being of others.
Here’s a great video that addresses this point: http://www.youtube.com/watch?v=FDSAAlrqAHM
May you be happy!
There are three essential qualities:
1) Bodhi mind: the vow to attain Buddhahood.
2) Compassion: the compassion to liberate all sentient beings (which implies the delay of self-liberation).
3) Emptiness as skilful means: the wisdom of emptiness required for self and others-liberation and for long diligent practices.