Adverb and Preposition

Adverbs are words or groups of words which tell time, place, frequency or manner.
	I ate my lunch yesterday.		She went there.
	I ate at that restaurant last week.		She went downtown.

Prepositions are usually followed by objects in prepositional phrases. They can also be used to indicate time, place, frequency, duration, reason, manner, or to show contrast.
	I ate my lunch at noon.		She went to the store.
	I ate in the cafeteria.		She walked into the house.

*Do not use adverbs as objects of prepositions.

	Incorrect:		Correct:
	I went to somewhere.		I went somewhere.
	I was busy at last night.		I was busy last night.
	John works in downtown.		John works downtown.
	She came to home on yesterday.		She came home yesterday

Be careful with words such as home, downtown, today, next/last week, etc. which are sometimes used as adverbs and sometimes used as nouns.
As adverbs As nouns
	I will go back tomorrow.		Tomorrow is another day.
	She went home last night.		They built a home in Oregon.
	Next week I will travel to Iowa.		Next week is my vacation.