Should there ever be a hall of fame for professional AutoCAD users these immortal words should be inscribed on the entry portals to inspire and promote greatness.

Always draw full-size.

Always use OSNAPS to create accurate geometry.

Always draw entities with the properties of "BY Layer".

Always create a separate layer for geometry that needs to be a different color or grouping.

Always name layers, blocks, X-refs, or any named style with descriptive words that are comprehendible by any discipline.

Always draw your full-size objects in Modelspace.

Always dimension in Modelspace.

Always use associative dimensions and associative hatching.  

Never override an associative dimension.  Always correct the geometry in order to change a dimension value.

Paperspace only contains Viewports, Titleblocks, titleblock information, and notes that are specific to the Paperspace layout.

Always use a Color-Dependant plot style, never use a named plot style.

Always purge un-used entities from a drawing.

Abide by the KISS principle: Keep It Short and Simple!