"Many persons," Sr. Lucia of Fatima explained, "feeling that the word penance implies great austerities, and not feeling that they have the strength for great sacrifices, become discouraged and continue a life of lukewarmness and sin." Then she said Our Lord explained to her: "The sacrifice required of every person is the fulfillment of his duties of his state in life and the observance of My law. This is the penance that I now seek and require."
It was in this same spirit that the Angel spoke to the children in 1916: "Offer up everything in your power as a sacrifice to the Lord in reparation for the sins by which He is offended, and in supplication for the conversion of sinners . . . More than all else, accept and bear with resignation the sufferings that God may send you." - Source
The duties of ones state in life is the ordinary way of sanctity, the 'little way', encompassing the practice of the virtues, and so on. Accepting the sufferings of daily life, the sacrifice of selfish self-love - that is penance. For instance, the virtue of temperance might be a good one to work on for many of us... More deeply, if you really feel you are not doing enough... the mortification necessary to practice prayer is perhaps the best penance after ones duties.
Exercise and yoga and dieting = self love.