For metaphors, the key is to draw on words that already have strong symbolic associations. So, if you just say "hate is a glove," your metaphor won't make sense. If, on the other hand, you say "hate is a jet black glove stretched tight over a pale hand," you have something you can work with. The color black is already associated with evil and negativity in our culture, and most people identify hate as a negative emotion. The term "pale" in turn is associated with sickness and decay. So, the metaphor says something along the lines of "hate is a negative emotion that can envelop and constrict (implied by "stretched tight") the soul (represented here by the hand), causing it to sicken and decay.
You can use this technique to create a comparison between just about any abstract concept, especially emotions, and any concrete noun. So,
Sadness is a cup
Sadness is a cracked china cup, sitting forgotten in a dusty cupboard.
Intelligence is a knife
Intelligence is a keen-edged machete slicing through thickets in a jungle of ignorance.
And so on. In each case, the main comparison involves words picked at random (sadness, cup; intelligence, knife) giving you some originality, but the supporting structure is rooted in familiar cultural symbols that make it easy for the reader to understand the metaphor.
Sean, EssayForum.com