Is it true that 'self' pronouns should generally used as subjects?

No, the 'self' pronouns are the reflexive pronouns, which are never used as the subject of a sentence. The reflexive pronouns 'reflect' back to the subject of the sentence; for example:

My mother made the dress herself.

The Browns replaced the roof themselves.

I did all the research myself.

The reflexive pronouns can also be used as intensive pronouns to emphasize the subject; for example:

My mother herself made the dress.

The Browns themselves replaced the roof.

I myself did all the research.