Pain, fatigue and musculoskeletal disorders may be the consequence of awkward and inadequate postures caused by the improper design of work activities and poorly designed workstations. The good design of workstations following the ergonomics principles is necessary to avoid these adverse effects. This study aimed to define a set of ergonomics principles for the design of assembly workstations for both left-handed and right-handed users. An experimental study was performed at the university laboratory involving both left-handed and right-handed users for the assembly of a centrifugal electric pump. The experimental study proved that left-handed and right-handed users differently interact with the objects in the space. Four fundamental ergonomics principles for the design of assembly workstations for both left-handed and right-handed users have been defined, based on the results of the laboratory test. The proposed principles help designers and practitioners during the design of assembly workstations, proving the importance of the ambidextrous design of workstations.