Parole officers, by definition, are interacting on a daily basis with convicted criminals who have been released ahead of their maximum sentence because of "good behavior" while incarcerated or because of prison overcrowding. Either way, at least with regard to individuals who had been serving time for a violent crime, any aspiring parole officer needs to be aware of the potential danger to him or herself.
An obvious recommendation for someone aspiring to that position, therefore, would be to take very seriously the training required of parole officers. Many prisoners, while undereducated, are nevertheless street-smart, and capable of convincing an untrained individual that they are on the right path while actually reconnecting with their old associates for the purpose of committing additional crimes. The recidivism rate for convicted felons is not good, and exconvicts who had been convicted of violent crimes are not likely to have had the violence indoctrinated out of them while in prison.
Another recommendation for an aspiring parole officer is to accept that you are entering a profession in which most of the people with whom you come in contact on a daily basis are, of course, criminals. As with some social workers and many police officers, the day-to-day immersion in the underside of society can be emotionally draining and can be very hard on family life. An inability to leave "the office" at "the office" and to bring home the frustrations of the day can have a very corrosive effect on one's spouse and children.
A final recommendation for an aspiring parole officer is to accept going in that it is not a lucrative field. Once again, as with social workers and police officers, the pay is not commensurate with the risk both to one's physical well-being and to one's mental well-being.