What are the best medical writer qualifications and training to get ahead?

What is the best training for becoming a medical writer? What types of ongoing training or certifications are necessary to be an effective medical writer?

What do non-traditional career paths look like?

There is not really a training or certification process, though some countries have national organisations which offer continuing professional development, and larger agencies sometimes have formal training. You basically need a degree and PhD in Life Sciences, an aptitude for writing (and actually have enjoyed writing your PhD thesis, papers etc), spelling and grammar. You would benefit from having published some papers or done some writing (blog, student paper) etc. Then you apply for trainee or associate writer positions.

There isn't a 'traditional' path per se - people may have just completed a PhD, done some post doctoral positions or maybe have trained as a clinician. Others get editorial assistant experience and try to transfer towards writing further down the line.