You will form the dative and accusative cases as you do all the others: add the appropriate ending to the stem you find by dropping the ending of the genitive singular.
Note that in all three declensions, the dative plural endings are identical to the ablative plural endings. In the second and third declensions, masculine neuters have identical endings except that neuter accusatives are always identical in form to the neuter nominative.
The new endings you need to commit to memory are listed here.
First declension:
Case
Singular
Plural
Dative
-ae
-īs
Accusative
-am
-ās
Second declension masculine:
Case
Singular
Plural
Dative
-ō
-īs
Accusative
-um
-ōs
Second declension neuter:
Case
Singular
Plural
Dative
-ō
-īs
Accusative
-um
-a
Third declension masculine or feminine:
Case
Singular
Plural
Dative
-ī
-ibus
Accusative
-em
-ēs
Third declension neuter:
Case
Singular
Plural
Dative
-ī
-ibus
Accusative
-
-a (-ia for i-stems)
Full examples
You now know all forms of first, second and third declension nouns! The following models illustrate complete declensions in the traditional order (nominative, genitive, dative, accusative, ablative).