Whenever your health is low and you find a fairy, take your bottle out and run into the fairy. While its circling you, swing your bottle. The fairy won’t heal you but will instead be captured inside your bottle.
Go to Castle Town when you are low on health. Complete the STAR game, which is played inside the big purple circus tent. Now talk to the three girls outside the tent and they’ll giggle and throw three hearts. Repeat as many times as you like.