Most first declension Greek nouns end in or η. All such nouns are feminine in gender. The long alpha is found only in words whose stems end in ε, ι or ρ. First declension nouns in /η are declined with the following endings:

Nominative in Nominative in -ᾱ
Singular Plural Singular Plural
Nominative (nom.) -αι -ᾱ -αι
Genitive (gen.) -ης -ῶν -ᾱς -ῶν
Dative (dat.) -ῃ -αις -ᾱͅ -αις
Accusative (acc.) -ην -ᾱς -ᾱν -ᾱς
Vocative (voc.) -αι -ᾱ -αι

* To decline any noun, you should take the genitive singular form (which can be found in a proper dictionary entry) and remove the ending; to that stem add the appropriate ending for the case and number required.

Nouns have persistent accent, as a general rule. However, the plural genitive of first declension nouns always takes a circumflex on the ultima. And when the accent of the genitive singular is on the ultima, both the genitive and dative will take a circumflex accent, singular and plural. In addition, the plural declension marker -αι is always counted as short for the purpose of determining accent.