Since the discovery of high-entropy alloys (HEAs) in 2004, a "renaissance in metallurgy" has begun. A significant number of novel alloys designed using the non-conventional multi-principal element strategy have been developed and exhibited superior properties over traditional alloys. This promising alloy design strategy has received great research interest and has evolved rapidly in the past two decades. The original HEA family has now broadened and become the complex concentrated alloys (CCAs) family to unlock its full potential for generating next-generation metallic materials. This dissertation has focused on the development of unifying processing strategies that can be generally applied to several typical novel microstructures of CCAs to achieve microstructure tailoring and properties enhancements with minimum compositional dependency for coping with the huge variety of CCA compositions. In particular, the enhancements were made through utilizing the state-of-the-art, heterogeneous structure strategy, for obtaining synergic effects. The research in this dissertation can benefit a major portion of existing CCAs in broadening their scopes of applications and expediting their adoption in industry. Furthermore, the findings in this dissertation are not limited to the CCA field, they can also be applied to various traditional metallic materials systems to further improve the performance of many important materials currently in service.