Declension of nouns in plural

Among declension rules of plural nouns there are some cases, which you should learn because they might seem unobvious to a foreign student.

For example, we've got used that when we decline neuter nouns, we get the form "Яблоко - Яблок" (an apple- apples) in plural. But when we decline such nouns as "небо" (the sky) and "чудо" (a miracle), there is the suffix -ЕС in plural that is untypical for neuter nouns. So we get the following form: "Небеса - Небесами", "Чудеса - о чудесах".

Here is another example. We've learned that masculine nouns in plural usually get the endings -И, -Ы. But there is a range of words, which are not applied to this rule, so you should use them correctly. Here are the examples of these words.

Остров - острова (an island - islands)
Доктор - доктора (a doctor - doctors)
Паспорт - паспорта (a passport - passports)
Адрес - адреса (an address - addresses)
Сторож - сторожа (a guard - guards)

Russian-speaking people also often mix up the endings -И(-Ы)/-А for nouns. You should just learn such words. You should also memorize noun declension in the genitive case, plural form. Pay attention, lexicalized words can be declined in different ways.

Апельсины - апельсинов (oranges)
Помидоры - помидоров (tomatoes)

Мандарины - мандаринов ( tangerines)
(Not "апельсин" and not "помидор"!)

But яблоки - яблок (apples)
(Not "яблоков")

Метры - метров (meters)
Грамм - граммов (grams)
Гектары - гектаров (hectares)

Полотенца - полотенец (towels)
Блюдца - блюдец (plates)
Места - мест (places)
Облака - облаков (clouds)
Стекла - стёкол (glasses)
Дела - дел (affairs)
Противень - противней (baking trays)