"Rend your hearts, and not your garments". This is a command that has been given to us. Jesus had a lot to say about the nature of fasting and mourning, as well as about celebration. We are to avoid prideful displays of our mortifications.
I have come to realize that a lot of who I am as an adult Christian was formed by my 4 years in Episcopal day school (grades 2 - 5). Daily morning prayer, twice weekly communion services, and Sunday School weekly exposed me to a lot of Scripture. I opened up my 40 year old and yellowing Book of Common Prayer this morning, and turned to the readings for Ash Wednesday. There it is - Joel. The Gospel from Matthew 6:16-21 sets out ground rules - "Be not, as the hypocrites, of sad countenance".
I was particularly struck by the Collect (short prayer, I think the word comes from recollection) of the day.
Almighty and everlasting God, who hatest nothing that Thou hast made, and dost forgive the sins of all those who are penitent; Create and make in us new and contrite hearts, that we, worthily lamenting our sins and acknowledging our wretchedness, may obtain of thee, the God of all mercy, perfect remission and forgiveness; through Jesus Christ our Lord. Amen.
Let us also pray in the words of Psalms 102 - "I have eaten ashes as if it were bread" and 103 - " The merciful goodness of the Lord endures forever".
Wear your ashes with humility, and remember that they are made from the Palms of last years triumph and celebration.