Today signifies the beginning of Lent. It is a time of penance and almsgiving. It serves as a opportunity to cleanse ourselves prior to the celebration of Easter. Making a "sacrifice" during lent might include "giving up" some favorite vice (video games, chocolate or basically anything that one would miss). I fast a lot during the normal seasons and a lot more during Lent. It is a very disciplined way to avoid excess. Try to fast during the Lent season regardless of your religious persuasion.
For a little more info on the history of Ash Wednesday, check out this info from the Catholic Encyclopedia
The Wednesday after Quinquagesima Sunday, which is the first day of the Lenten fast.
The name dies cinerum (day of ashes) which it bears in the Roman Missal is found in the earliest existing copies of the Gregorian Sacramentary and probably dates from at least the eighth century. On this day all the faithful according to ancient custom are exhorted to approach the altar before the beginning of Mass, and there the priest, dipping his thumb into ashes previously blessed, marks the forehead -- or in case of clerics upon the place of the tonsure -- of each the sign of the cross, saying the words: "Remember man that thou art dust and unto dust thou shalt return." The ashes used in this ceremony are made by burning the remains of the palms blessed on the Palm Sunday of the previous year. In the blessing of the ashes four prayers are used, all of them ancient. The ashes are sprinkled with holy water and fumigated with incense. The celebrant himself, be he bishop or cardinal, receives, either standing or seated, the ashes from some other priest, usually the highest in dignity of those present. In earlier ages a penitential procession often followed the rite of the distribution of the ashes, but this is not now prescribed.
There can be no doubt that the custom of distributing the ashes to all the faithful arose from a devotional imitation of the practice observed in the case of public penitents. But this devotional usage, the reception of a sacramental which is full of the symbolism of penance (cf. the cor contritum quasi cinis of the "Dies Irae") is of earlier date than was formerly supposed. It is mentioned as of general observance for both clerics and faithful in the Synod of Beneventum, 1091 (Mansi, XX, 739), but nearly a hundred years earlier than this the Anglo-Saxon homilist Ælfric assumes that it applies to all classes of men. "We read", he says,
in the books both in the Old Law and in the New that the men who repented of their sins bestrewed themselves with ashes and clothed their bodies with sackcloth. Now let us do this little at the beginning of our Lent that we strew ashes upon our heads to signify that we ought to repent of our sins during the Lenten fast.