Let’s get the obvious one out of the way first, four leaf clovers are said to bring good luck (especially if placed in the shoe).
The rhyme goes:
one leaf for fame, one leaf for wealth,
One for a faithful lover,
One leaf to bring glorious health.
Are all in a four leaf clover
On the other hand a five leaf clover (is there such a plant?!) is bad luck.
The white clover was used to ward off and remove evil spirits and ghosts. It can be worn as a talisman, or put in the four corners of a house. It is said to be also good to remove hexes if scattered.
Clover (both three and four leaf) was also said to enable communication with fairies and the underworld.
To talk to the fairies you must wear clover in your hat. To see them you need to cover yourself in an ointment made of a four leaf clover, or carry a charm made of seven grains of wheat and a four leaf clover.
If you’re having trouble finding them, a field of clover is said to attract fairies.