Colloquial Spanish we should avoid

If we do not raise our brows, or frown, or make a face when someone is talking to us in Spanish and we understand everything, we may say that it is good Spanish. The type of Spanish that brings out the best of the language and attains its main purpose: communicate ideas easily and efficiently is always the one to learn.
We must skirt vernacular idioms and words, and shirk from popular slang and colloquial expressions.
Thus, in Spanish, we should never utter:
"Na" instead of "nada" "No quié na."
"Pa" instead of "para" "Este pan es pa ti."
"Señá" instead of "señora" "La señá Dolores."
"Mu" instead of "muy" "La paella está mu güena."
"Güeno" instead of "bueno" M´hijo e' mu güeno."
"Bailemos" instead of "bailamos" "Ayer mi Pedro y yo bailemos mucho."
"Detrás mío" instead of "detrás de mí" "El Paco va detrás mío siempre."
"Comío" instead of "comido" "Hemos comío mu bien."
And there is more, much more... but if we prick up our ears we will detect many additional "popular" ways of speaking Spanish.
"M´ha dicho," "sausté" instead of "sabe usted", "m´hablao" instead of "me ha hablado", "mijito" instead of "hijo mío." remind me of the Tagalog expression meaning "how are you" or "hello": "kumostá" (del español "como está.")