"I do not consider him a good father."

[BrandonCas821536]

What is the rule on use of "za," please? When should it be used and for what purpose?

[VladaFu]

For various purposes. Generally, za means "behind", sometimes "after" sometimes "for". Here it is connected with the verb: "považovat někoho za"="consider somebody (as) something" Different verbs require different prepositions and you have to learn them individually.

[venik212]

Is it grammatically wrong to put nepovažuju after Ja, instead of at the end of the sentence?

[VladaFu]

Observe the second position rule for ho and report the complete sentence next time.