Garnishes don't have to be fancy, and can be as simple as a sprig of fresh cilantro, a sprinkling of toasted sesame seeds, a few rings of sliced green onion, a wedge of fruit, or a small chile pepper, whatever is on hand and suits the recipe.
Garnishes should be edible and must relate to the flavor of the dish.
Set the garnish aside when preparing the recipe so it's handy for when you're ready to present the plate.
Try not to repeat the same garnish on more than one recipe.
Use your imagination!