According to the case suffixes, nouns in Serbian can be grouped into three or four declensions (the order and number hasn't been established yet). I'll list the three most commonly presented ones, starting from the most complex one, which is often subdivided, depending on the noun gender and its stem ending:

1. Declension:

Masculine nouns ending in a consonant
Neuter nouns ending in -o or -e

*Note that Masc. nouns in Sg. Acc. is the same as the Genetive if the noun denotes an 'animate concept', like human being or an animal, while the 'inanimate' ones are objects, but also plants and groups of people or animals (like 'a people'= 'narod' or pack (of wolves)= 'čopor')

** All Neuter nouns have the same form for Nominative, Accusative and Vocative, which is really great :o)

*** With Masc. nouns ending in palatal 'j, lj, nj, č, dž, đ, ć, š, ž'
a/ in Sg. Instrumental case it will end in 'em', instead of 'om'
b/ in Sg. Vocative case it will end in 'u' instead of 'e'

	ANIMATE	ANIMATE	non-ANIMATE	non-ANIMATE
Sing.
	non-palatal ending	palatal	non-palatal	palatal ending
Nom	DOKTOR	PRIJATELJ	BROD	ČEKIĆ
Gen	DOKTOR-A	PRIJATELJ-A	BROD-A	ČEKIĆ-A
Dative	DOKTOR-U	PRIJATELJ-U	BROD-U	ČEKIĆ-U
Acc	DOKTOR-E	PRIJATELJ-A	BROD	ČEKIĆ
Voc	DOKTOR-E	PRIJATELJ-U	BROD-E	ČEKIĆ-U
Inst	DOKTOR-OM	PRIJATELJ-EM	BROD-OM	ČEKIĆ-EM
Loc	DOKTOR-U	PRIJATELJ-U	BROD-U	ČEKIĆ-U

****The pattern for Plural being the same for all the forms:

Nom	DOKTOR-I
Gen	DOKTOR-A
Dative	DOKTOR-IMA
Acc	DOKTOR-E
Voc	DOKTOR-I
Inst	DOKTOR-IMA
Loc	DOKTOR-IMA

*****Elongated Plural can be seen in the majority of one syllable and a good part of two syllable nouns. In the plural they get 'OV' or with palatal ones 'EV':

	Elongated' = longer form
Nom	STAN-ov-I
Gen	STAN-ov-A
Dative	STAN-ov-IMA
Acc	STAN-ov-E
Voc	STAN-ov-I
Inst	STAN-ov-IMA
Loc	STAN-ov-IMA

******* Sometimes, if the noun ends in -c, -s, -z or -t, there is an ending in -ev (e.g. vicevi (jokes), nosevi (noses) , putevi (roads) )

Well, as you can see, this is just the beginning of the story about Noun Declensions. If you are learning Serbian, I'd like to ask you if you find it easier to learn the language in this 'grammar oriented' fashion, or simply 'by ear'?