I am still building my experience; my first job was recording for an English-learner's course, the TOEC, reading the practice sentences that accompany the textbook.
But I practice constantly on our home recording equipment--reading copy out of magazines, repeating ads I've heard on the radio, even working on my dialects for stage productions.
I had private coaching from Terry McGovern in the San Francisco Bay Area to learn voice-over; we worked together for several months and he produced my voice-over demo.
I also have many years of training as an actor.
In addition to my acting and voiceover training and facility with dialects, I hold a PhD in English from UC Davis where I taught for seven years--five as a graduate student and two as a lecturer. This teaching experience helped to develop my vocal skills.