Bess,
Normally with Sage, the harvest is the pruning. This is usually not started until the second year of growth. Just before the plants flower, cut them back severely, down to 4-6". This promotes branching. You can generally get 2-3 harvests for about 5 years before the plants start to decline, then replant. If you let a couple set seed in the 3rd year, you'll have replacements ready. Bumblebees love sage flowers. Seed takes 2-3 weeks to germinate, sometimes faster. It can also be propagated from cuttings. Even if you don't need it, harvest it anyway. Might be able to sell or give it away near the holidays. The dried leaves store best whole. Sage also has antibacterial, antiviral, and antifungal properties. Sage tea is effective against sore throat, something use the extra harvest for.
Rick

Actually, you could let it grow until it's ready to bloom first. This will give it a chance to make food for the roots, and allow you to compensate for any damage caused by the winter or an odd spring. This way, the first pruning can also be the harvest, with the plants only getting bushier from there.
Rick