cut garnishes

very easy

Citrus:

• paring knife
• zester   (the type that's often attached to a channel knife)
• Y-peeler
• channel knife

easy

Citrus:

• twist   [2]
• double twist ^†
• cross-bow ^†
• bird ^†
• star
• four-leaf clover
• triangle fence
• and the related sun

† High bang-for-the-buck, in terms of having a lot of visual interest while not requiring a ton of work.

harder

• bird, a variant of cross-bow