Prepositions are words or sets of words that indicate location, comparison or time and indicate a relationship between a noun / pronoun and the rest of the sentence.

eg: I’ll meet you at 5 o’clock (‘at’ is the preposition, here it is indicating time)
eg: I’m swimming in the pool (‘in’ is the preposition, it indicates location)
eg: You are like my maths teacher! (‘like’ is the preposition, it indicates a comparison between two things)

Here are some general rules about prepositions:

1. Prepositions generally come before the noun or pronoun
2. Prepositions must always be followed by a noun or pronoun, never by a verb
3. ‘Like’ can’t be followed by a verb and ‘As’ must be followed by a verb
4. Use ‘as ; as if ; as though ; the way’ instead of ‘like’
5. Don’t confuse ‘in’ and ‘into’. ‘In’ indicates location whereas ‘into’ indicates movement
6. Never substitute ‘Have’ for ‘Of’