If growing indoors, a fertilizer once a month can be good.
Prune basil back regularly to encourage continued growth and thus allow for more growth.
Harvest by pinching off individual leaves.
For indoor plants, be sure to water them regularly to keep the soil evenly moist.
To extend the harvest season pinch off flowers as they appear.
For indoor mint, place plant where it will receive morning light and away from drying heating elements.