There is one very simple rule about prepositions. And, unlike most rules, this rule has no exceptions. Rule A preposition is followed by a "noun". It is never followed by a verb. By "noun" we include: * noun (dog, money, love) * proper noun (name) (Bangkok, Mary) * pronoun (you, him, us) * noun group (my first job) * gerund (swimming) A preposition cannot be followed by a verb. If we want to follow a preposition by a verb, we must use the "-ing" form which is really a gerund or verb in noun form.

You put prepositions where you normally put them. No extra rules.