Musar zu Tehillim 48:15

And in the Midrash (Vayikra Rabba 11:9) on the verse (Tehilim 48:15) "He shall lead us in youth" - [filled] with zeal as young maidens, as it is said: "in the midst of maidens playing the timbrels" (Tehilim 68:26) ["in youth" and "young maidens" are related words in Hebrew].

The means through which Zeal is acquired are the same ones through which Watchfulness is acquired, and their levels are likewise similar as I wrote earlier.