Prepositions indicate relationships between words or ideas. Most prepositions deal with location and are easy to learn.

above
inside

beside

near

up

before*

with

into

between

like

despite

below
outside

beyond

nearby

down

after*

without

out (of)

among

as

in spite of

over
around

behind

by

toward

during

within

off

except

than

beneath

under
through

in front of

next to

along (side)

since*

until*

upon

but*

about

underneath

*These can also be used as conjunctions.
Some prepositions, however, have more than one meaning and can be very confusing.
in
to
on
from
at
for
of

Preposition and Time
General

In (year, month) In 1989, in December
On (day, date) On monday, on Dec. 14, 2001
At (time) At 7:00, at 8:30
During (decade, long time period) During the 1960s, during the 20th Century

Specific Time: "When?" (Use simple tenses.)
When did you eat your breakfast? I ate my breakfast at 9:00.
When were you born? I was born in 1979.
When is your birthday party? My birthday party is on Friday.
When will you graduate? I wil graduate in June.

Ongoing Action
Mr. Barnes is watching television now.
While he was watching television, the phone rang.
He will be watching television tonight when his wife gets home.
Duration: "How Long?"
How long have you been in the U.S.? I have been here since 1999/for two years.
How long were you in California? I was in California for three weeks.
How long will you be in Maine? I will be there for a month.

Completed Action
I have finished my homework already. (before now)
After I had finished my homework, I started to cook dinner.
I will have finished my homework, when I start to cook dinner.
Notes:
In + (amount of time) usually refers to the future: I will see you in two days (from now).
But it can also indicate a length of time: I finished the job in two hours.

Ago follows time word(s) and is used to indicate the amount of time before the present:

I called her two weeks ago. She returned my call five minutes ago.

Words indicating actions occurring at the ?same? time (or nearly the same time)
When When I was in high school, I had a car.
As soon as As soon as I got to the theater, I looked for a seat.
Once Once I finish my geometry, I will start studying chemistry.
The moment (that) The moment (that) I saw her, I knew who she was.

Words indicating actions occurring at ?different? times
Before Before my husband left, I had already packed his bags.
After After she eats her dinner, Ms. Warner will go shopping.
By the time By the time I get to Denver, I will have traveled 200 miles.
Until I cleaned the house until my wife came home.

See also:
JustSomeLyrics
77
77.76
John Pizzarelli Tenderly Lyrics
Iorio & Flavio Vírgen de los Muertitos Lyrics