The Pharisee and other religious groups of that time had their own voluntary fasts. The Pharisees in particular would fast twice a week. Now, these were not fasts commanded by the law but they were voluntary fasts of devotion. There were fasting times amongst the people of Israel that were mandated in the scriptures but they were public fasts and they were common fasts (as lent is a common fast). So there would be no social cache showing you were fasting when the people of God were fasting corporately and indeed you have instruction for the people too wear sackcloth and ashes in the scriptures during those public fasts... But when people make a private fast, they make their own personal, devotional decisions about fasting quite apart from what the church has in its rhythm of the liturgical year then they are not to make a big deal of that.
It is that time when we prepare for the joys of Easter. Where, like Christ, we go through the valley of the shadow of death before we reach the light at the end of the tunnel so to speak. The prayer book in todays service (the penitential service before Mass designed specifically for Ash Wednesday) says we are to observe Lent by self examination and repentance, prayer, fasting, self denial and by reading and meditation upon Gods holy word. Those are the traditional ways to observe Lent. We examine ourselves even more soberly and seriously than we normally would and think about the past year, what we have done wrong and ways we can improve.
In doing this we are able to focus the mind more on things of the spirit, as things of the flesh are to fall into the background more. Not because there is something wrong with eating, we have to eat, eating is a good thing. By doing less of these things which in itself is good we are able to focus more on the things that are best.
May God prepare our paths and grant us the grace
to follow through with our good intension
as we begin Lent.