When a conjunctive pers. pronoun follows the verb, the subject pronoun must also follow, as—
Dígolo yo (not yo dígolo): I say so.
Otherwise the position of the subject pronoun in relation to the verb is very arbitrary, the general practice being, of course, to put it before unless the sentence is interrogative.
The conj. pronouns nos and os following a verb in the Imperative mood require the elision of the s and d termination of the verb, as—
Escribámonos: Let us write to each other.
Escribíos: Write to each other.
Conjunctive pronouns are used to substitute the possessive adjective before parts of the body or articles of dress, as—
Me quebré el brazo: I broke my arm.
Se lastimó el dedo: He hurt his finger.
Se puso el sombrero: He put on his hat.