Medieval philosopher and theologian Thomas Aquinas asks in his Summa Theologiae, "Whether thankfulness is a virtue, distinct from the other virtues?"
For him, the answer is yes, because thankfulness is "a special part of justice." Giving thanks to our benefactors, those who have given us a particular and personal favor, is an issue of obligation, or justice. We owe gratitude to them, and this is different from the related virtues of religion (owed to God), piety (owed to parents), and observance (owed to those who excel in dignity). We are left with thankfulness as a virtue distinct from these related excellences of character. Thankfulness is a matter of justice.
The point, I take it, is that Thomas believes that gratitude is important in a variety of ways, related to God, parents, excellent human beings, and finally those who have benefitted us via a favor of some sort. We owe something to all of these persons, and perhaps the upcoming holiday is a good day to at least partially seek to fulfill that obligation.
There are many ways to do this, first by expressing thanks to those people in our lives who deserve it. Perhaps a spouse, friend, parent, or child. Perhaps a teacher, minister, or coach deserves a word of thanks. I've occasionally sent a note to authors who have made a difference in my life, which is much easier to do these days given the ease of access via the Internet. Perhaps for you an expression of gratitude to God is appropriate.
If thankfulness is truly a virtue, then its expression is not only a matter of justice in relation to others. It is also part of a good and fulfilling life for the person who has this good character trait.