russiangrammar:

If the noun is in the genitive, the adjective describing it must also be in the genitive.

Adjectives describing masculine/neuter nouns:

• Unstressed adjectives: -ого

BUT if the stem ends in ж, ч, ш, щ, ц (remember the second spelling rule) then the ending is -его.

e.g. паспорт английского (хорошего) актёра the English (good) actor’s passport

      недалеко от маленького поля not far from the small field

• Stressed adjectives: -ого

e.g. директор Большого Театра the director of the Bolshoi theatre

• Soft adjectives: -его

e.g. цена синего дивана the price of the blue sofa

You might recognise these endings because they’re exactly the same as masc. sing. animate accusative endings! Life just got like, 0.1% easier.

Adjectives describing feminine nouns:

• Unstressed adjectives: -ой

BUT if the stem ends in ж, ч, ш, щ, ц (again, see the second spelling rule) then the ending is -ей.

e.g. паспорт английской (хорошей) актрисы the English (good) actress’ passport

• Stressed adjectives: -ой 

e.g. директор большой компании the director of the big company

• Soft adjectives: -ей

e.g. цена синей рубашки the price of the blue shirt

Genitive plural adjectives:

Endings are the same in all three genders.

• Stressed and unstressed adjectives: -ых

UNLESS their stem, ends in г, к, х, ж, ч, ш, щ (see first spelling rule)

Examples of the ending -ых

паспорта молодых туристов the passports of the young tourists

книги современных писателей the books of the modern writers

фотографии иностранных курортов the photographs of foreign resorts

• The genitive plural adjective ending is -их if:

1. the adjective’s stem ends in г, к, х, ж, ч, ш, щ (see first spelling rule)
2. the adjective is soft (e.g. синий blue)

Examples of the ending -их

паспорта английских туристов passports of English tourists

книги древних писателей books of the ancient writers

фотографии наших друзей photographs of our friends