Today we observe the first of the winter Ember Days, which always falls on the Wednesday following Gaudete Sunday. Doesn't sound familiar? Don't worry, you're not alone: Ember Days are one of those parts of the liturgical calendar that somehow got lost in the kerfuffle following the Second Vatican Council, but bringing back the observance at home is simple!
Basically, the Ember Days are four sets of three days--Wednesday, Friday, and Saturday--marking the four seasons of the physical year. They are days of penitence (fasting, partial abstinence, prayer), but are also meant to focus on thanksgiving for the natural world. Traditionally they have also been periods particularly set aside for prayers for priestly vocations, and are a popular time for ordinations.
How can you observe the Ember Days this season? It doesn't have to be something big. We are having smaller, meatless meals today, Friday (obviously), and Saturday, and will be adding extra prayers for vocations, and for the priests and seminarians we know.
There is an excellent explanation of Ember Days at Why I Am Catholic, which I strongly recommend for a more in-depth look at the hows and whys of this observance: