Here’s some tips I’ve learned to make really clean faces/edges:
a) make sure your base mesh is very, very simple and clean, and the topology flows the same as the shapes you’d like to create.
b) rely on the smothing that subdivision does to get your smooth curves, rather than importing an object with all those curves built in.
c) NEVER use the regular “freehand” brushes for anything. They’re just inherently messy. Instead use deformers and opaque masks.
b) pay around a lot with when and where to crease an object. This is probably the most important concept to grasp.
c) Work on as low of a subdivision as humanly possible. If you want a sharp edge, crease it until later. Smooth sweeping curve? don’t crease at all.
Basically, you need to control the shape of an object with nothing but crease levels, simple masks and deformers. No brushes. If you can do that, you’ll have perfectly machined looking stuff.