Material extrusion is one of the most commonly used additive manufacturing techniques which utilizes thermoplastics as the building material. The quality and performance of parts produced via material extrusion depends highly on the process parameters selected. This paper reviews the work done by various researchers on optimizing key process parameters like extrusion temperature, layer thickness, infill percentage, infill pattern etc. in material extrusion 3D printing using thermoplastics like PLA, ABS and nylon. The effects of these parameters on properties like surface roughness, dimensional accuracy, mechanical strength are discussed. Statistical tools like Taguchi method and response surface methodology that have been applied for parameter optimization are also reviewed. The review highlights the need for further process optimization studies considering part design, build orientation and post processing to unleash the full potential of material extrusion 3D printing..