Use the Bug Net or Big Bug Net to capture the following bugs in the Overworld. Bring them to the Potion Lady's husband in the Skyloft Bazaar along with the base potion to upgrade it.

Air Potion+ (20 Rupees): 2 Sky Stag Beetles, 2 Skyloft Mantises, 2 Lanayru Ants
Guardian Potion+ (40 Rupees): 1 Faron Grasshopper, 2 Eldin Rollers, 3 Blessed Butterflies, 3 Starry Fireflies
Heart Potion+ (20 Rupees): 1 Woodland Rhino Beetle, 3 Blessed Butterflies, 1 Volcanic Ladybug
Heart Potion++ (30 Rupees): 3 Deku Hornets, 3 Blessed Butterflies, 1 Sand Cicada, 1 Eldin Roller
Revitalizing Potion+ (20 Rupees): 3 Deku Hornets, 2 Skyloft Mantises, 2 Woodland Rhino Beetles
Revitalizing Potion++ (30 Rupees): 3 Lanayru Ants, 2 Woodland Rhino Beetles, 1 Gerudo Dragonfly, 1 Sand Cicada
Stamina Potion+ (20 Rupees): 3 Volcanic Ladybugs, 2 Sky Stag Beetles, 2 Gerudo Dragonflies, 1 Faron Grasshopper