Articles

-->A description/A defining feature follows the preposition 'DE'

Example: Un livre d'histoire  - Answers the question.. 'What kind of book?' - 'History book'

              Un jus d'orange -    Answers the question.. 'What juice' - 'orange juice'

-->A Possession uses the preposition 'Du/De la/De l'/Des'.

Example: Le livre de l'étudiant- Answers the question.. 'Whose book' 

              whereas - le livre d'étudiant- Answers the question... 'What book?'  -'Student book' (A book aimed at students.)

Note : For proper nouns, we just use 'de or d' '. Example: 'La voiture de Katie.' - ' La voiture d'Isabelle.'

-->Quantities:

1)These take only 'De' when its Unspecific.

Example: Beaucoup d'argent - A lot of money, Une tasse de thé - A cup of tea

'Beaucoup' and 'tasse' are measures.

2) The specific ones take 'Du,De la,De l',Des'

Example: Beaucoup des gâteaux que tu as mangés, étaient préparés par moi - Lot of the cakes(Most of the cakes) that you ate, were prepared by me

we say 'Beaucoup des gâteaux' because 'des gâteaux' represents the certain cakes prepared by a certain person.

-->before adjectives:

When describing unspecific nouns use 'De or Des'

Ex:
Affirmative form : Je veux acheter de /des nouvelles chaussures. (but 'des' is better.)
Negative form : Je ne veux acheter de / des nouvelles chaussures . (but 'de' is better.)

After adjectives describing specific nouns use 'Du,De la,De l',Des'

On veut profiter des nouveaux accords - We want to take advantage of the new agreements (New agreements describes a set of specific agreements)