Harrison:

I read carefully the instruction of your form in English: “Important – Please Read Carefully!

This is my analysis.

Some people don’t use the “Por favor” (Please) in Spanish, but I think is a polite way to give an instruction or warning.

Some of your translations are very good:
¡IMPORTANTE - POR FAVOR LEA CUIDADOSAMENTE!
¡IMPORTANTE - POR FAVOR LEER CUIDADOSAMENTE!

You know the rules of the Spanish grammar. In all your samples you use the exclamation marks for begin and end the expression. This is excellent. In Spanish, all the exclamation sentences have a start-exclamation mark and end-exclamation mark. Very good from you!!! (You write better than a lot of Spanish natives.)

We continue with the analysis:

Some people in Mexico don’t put “¨por” before “favor” but it is wrong and unpolished. The “por” helps to be more polite and friendly. And in Spanish language, if you write good, you have to say: “por favor”. It is the equivalent to say “please” in English.

You can say: “lea”, “léase”, o “leer”. “Lea” is more personal than “leer” but both terms are right. “Léase” is very good but longer than “lea”. When you write the instruction to fill a form you are not writing a speech.

It is good “cuidadosamente”, but you can exchange this adverb for the expression “con atención”.

After this analysis, I would like to write the different options that we have on the desk. These are the options:

¡IMPORTANTE - POR FAVOR LEA CUIDADOSAMENTE!
¡IMPORTANTE - POR FAVOR LEA CON ATENCIÓN!
¡IMPORTANTE - POR FAVOR LÉASE CON ATENCIÓN!

¡IMPORTANTE - POR FAVOR LEER CUIDADOSAMENTE!
¡IMPORTANTE - POR FAVOR LEER CON ATENCIÓN!


You are in the right way. Now, you can decide what expression you like more.

Thank you.

Domingo