design of linear electro mechanical actuator

The goal or performance definition is quite helpful in the design of an actuator, if you seek satisfactory results.

The main parameters are the ones generally described in actuator data sheets, add to that your specific application constraints.

1000's of products do exist on the market, using 10's of technologies in many different configurations, and still sometimes you can only find one or two to do the job you need.

Generalizations would be quite useless here, be specific on your application.

Speed, force, travel, and power input. Design it in 3D CAD rather than on paper - much easier. Or just buy one.