A considerable weight reduction in thermoset-based composite is attained by replacing mechanical fasteners with a structural adhesive during the secondary bonding. The quality of this adhesively-bonded joint greatly depends on the surface preparation strategies applied to the mating composites as they influence the surface morphology, topography, interface composition, and mechanical performance of the adherend–adhesive interphase. We reviewed the recent progress of surface preparation strategies generally employed for the aerospace or automotive-grade thermoset composites (carbon/epoxy and glass/epoxy). Then, we briefly reviewed the role of each of them in promoting adhesion mechanisms, i.e., mechanical interlocking, adsorption/chemical bonding, and diffusion. Subsequently, we analyzed qualitatively and quantitatively the effects on indicators associated with surface characteristics of the treated surface and mechanical performance metrics. Finally, we discussed two emerging solutions, namely substrate patterning, and adhesive tailoring. Our analysis shows that creating heterogeneity in the composite adherends or adhesive enables effective tuning of the joint performances.