Prepositions  form a small but very important word class. We use prepositions very frequently. In fact, the prepositions to, of, in, for, on, with, at, by, from are all in the top 25 words in English. If you can understand and correctly use prepositions, it will greatly improve your fluency. And remember, there are not very many prepositions. There are only 150 prepositions and we only use about 70 of these commonly. The following rules will help you understand and use prepositions correctly.

1. A preposition must have an object

All prepositions have objects. If a "preposition" does not have an object it is not a preposition—it's probably an adverb . A preposition always  has an object. An adverb never  has an object. Look at these example sentences:

  • They are in  the kitchen. (preposition in  has object the kitchen)
    Please come  in. (adverb in  has no object; it qualifies come)
  • There was a doorway before me. (preposition before  has object me)
    I had never seen it  before. (adverb before  has no object; it qualifies seen)
  • I will call after work. (preposition after  has object work)
    He called soon  after. (adverb after  has no object; it qualifies called)

2. pre-position means  place before

The name “pre position” indicates that a preposition (usually) comes before  something (its object):

  • I put it in the box.

But even when a preposition does not come before its object, it is still closely related  to its object:

  • Who  did you talk to ? / I talked to Jane.

3. A pronoun following a preposition should be in object form

The noun or pronoun that follows a preposition forms a ‘prepositional object’ . If it is a pronoun, it should therefore be in the objective form ( me, her, them), not subjective form (I, she, they):

  • This is from my  wife and  me.
  • That’s  between  him and  her.
  • Mary gave it to  them.

4. Preposition forms

Prepositions have no particular form. The majority of prepositions are one-word prepositions, but some are two- or three-word phrases known as complex-prepositions:

  • one-word prepositions  (before, into, on)
  • complex prepositions  (according to, but for, in spite of, on account of)

5. to  preposition and to  infinitive are not the same

Do not confuse the infinitive particle “to” (to sing, to live) with the preposition  “to” (to London, to me).

to  as preposition

  • I look forward to lunch
    I look forward to seeing you
    I look forward to  see you
  • They are committed to the project.
    They are committed to keeping the price down.
    They are committed to  keep the price down.
  • I am used to cars.
    I am used to driving.
    I am used to drive.

to  as infinitive particle

  • They used to live in Moscow.
  • They love to sing.

6. The golden preposition rule

A preposition is followed by a "noun". It is NEVER followed by a verb.

sources : Original Link