Rosh Hodesh, literally "head of the month," or the first day of the new month, is sort of a half-holiday. There's not much to it, as holidays go, other than the extra liturgical material we added this morning: an extra paragraph in the Shaharit Amidah, an extra aliyah during the Torah reading, an extra Amidah (Musaf, which means "extra") at the end, and recitation of the extra Psalms of Hallel.
How should one, therefore, celebrate Rosh Hodesh? Well, maybe with something extra, just as a reminder. An extra bagel, perhaps. Or an extra hug to the ones you love. Hodesh tov!