How do I break into SDR roles?

I am looking to take the plunge into becoming an SDR. I have experience in customer service as well as client retention in the telecommunications industry. I've done my due diligence and brought myself up to speed in the fineries of this position and what to likely expect of myself. I have looked through the forum and saw many advising that people in a similar position to mine should take a more active approach and find the hiring manager and other key decision makers in the hiring process. I was wondering would I do this before applying, after applying or not applying at all?