View

Fit view to object: Numpad .

Show/Hide Objects

Source
Hide selected objects: h
Hide unselected objects of the scene: Shift-h
Show hidden objects: Alt-h

Object

Set object origin point (center by default)

Source
Set “cursor” to object corner, than click “Object -> Set Origin -> Origin to 3D Cursor”.

Set object size (dimentions)

Open “Properties” panel (press n key).

Scene

Set grid size to millimeters

Source

Set units to millimeters

Panel

Toggle “Properties” panel: n