SALE, SAIL Sale is either offering something for purchase ("for sale") or offering it at a special price ("on sale"); sail is part of a ship or boat.
SELL, CELL Sell is to exchange for money; cell is a small room.
SCENE, SEEN Scene is place where something happens; seen is past participle of see. "Yet he had seen nothing suspicious at scene of accident." (Of course you wouldn't write a sentence like that; two words make for a clumsy combination. I would probably replace "scene" with "site".)
SITE, SIGHT, CITE Site always refers to location or place: building site; archaeology site. "We will site house to take advantage of panoramic views." Sight always refers to vision, as in cliche "a sight for sore eyes". "We sighted two horsemen coming over hill." "It was a sight I would never forget." "She feared she might lose her sight." Cite means to summon, or to refer to a source, as in following sentences: "I was cited as a witness to accident." "He cited in his defence an incident in which these same people were involved."
SOME TIME, SOMETIME This is a common confusion. Some time is a period of time and sometime means at some time not specified. "Some time ago you promised to introduce me to your brother." "Sometime when you're not busy we must do this again."
STATIONARY, STATIONERY Stationary means standing still. Stationery refers to writing paper.
STATUE, STATUTE, STATURE Statue is a carved or moulded likeness; statute is law; stature means height or status.
STRAIGHT, STRAIT Straight means without bends; strait is a passage of water.
TENANT, TENET Tenant is one who rents a property; tenet is a principle or belief.
THERE, THEIR, THEY'RE There is a location: "Put it over there." Their is possessive of they: "their coats" They're is short for they are: "They're unlikely to miss seeing them." So: "They hung their coats over there by door where they're unlikely to miss seeing them on their way out." Dreadful sentence I know, but at least it demonstrates correct usage for all three words.