I look up reference photographs! I don't know what kind of machinery you're trying to draw, but you can usually find decent pictures if you just google "[type of machinery]+ínside" or something like that. Find a good picture if what you're looking for, and reference that when you draw.
Since it's machinery, you should be able to do google-searches for blueprints of them too, which give you a VERY detailed drawing of exactly how all of it fits together.