Niche has several definitions but is most often used to describe a place or position most suitable for a certain person or thing. One can find one's niche. Golfing is Tiger Woods niche.
A cliche is a phrase that is so over used that it loses it's meaning. It often reflects very popular sentiment. Cliches are normally associated with a lack of sincerity. "Sadder but wiser" and "You get what you pay for" and what not are examples of cliches.
From dictionary.com...
cli·ché /kliˈʃeɪ, klɪ-/ Pronunciation Key - Show Spelled Pronunciation[klee-shey, kli-] Pronunciation Key - Show IPA Pronunciation
–noun
1. a trite, stereotyped expression; a sentence or phrase, usually expressing a popular or common thought or idea, that has lost originality, ingenuity, and impact by long overuse, as sadder but wiser, or strong as an ox.
2. (in art, literature, drama, etc.) a trite or hackneyed plot, character development, use of color, musical expression, etc.
3. anything that has become trite or commonplace through overuse.
4. British Printing.
a. a stereotype or electrotype plate.
b. a reproduction made in a like manner.
–adjective
5. trite; hackneyed; stereotyped; clichéd.
niche /nɪtʃ/ Pronunciation Key - Show Spelled Pronunciation[nich] Pronunciation Key - Show IPA Pronunciation noun, adjective, verb, niched, nich·ing.
–noun
1. an ornamental recess in a wall or the like, usually semicircular in plan and arched, as for a statue or other decorative object.
2. a place or position suitable or appropriate for a person or thing: to find one's niche in the business world.
3. a distinct segment of a market.
4. Ecology. the position or function of an organism in a community of plants and animals.
–adjective
5. pertaining to or intended for a market niche; having specific appeal: niche advertising.
–verb (used with object)
6. to place (something) in a niche.