I m suppose this question is for a mechanical engineer who just starts or to start his career.
You have to be friendly and talk to your machinist and any respective shop techs. You might have a fancier title or degree, but that makes you nothing matter from a mechanical engineer’s point of view. Small discussions on how to make a part more easily machinable/mouldable/etc. can save thousands of dollars and make you both appear good. In this process, you might even learn something. One more thing I want to tell you that if want to know more about mechanical engineering you should visit ASME site, this site has lot’s of information for mechanical engineers
As a new mechanical engineer you should try to learn the basics related to areas of mechanical engineering and you should have curiosity to know in depth. You should learn the relevant software available in this field. Most important thing improve your communication skills.