The preparation process of the nanocomposites and nanofluids strongly affects their general physical properties and stability in general. They are very sensitive with respect to the quality of the preparation process which should be obtained carefully to produce quality and reliable homogeneous samples. This paper provides a useful analysis in different preparation procedures with the focus on the nanoenhanced phase change materials (NEPCM) and fluids (nanofluids) due to their wide application areas. The preparation processes were identified and categorized together with the key parameters that have an important impact on the preparation process in general. The main problems and issues during the preparation process were discussed and elaborated in detail, gained by a detailed analysis of commonly applied preparation procedures. Since the preparation process of both nanofluids and nanocomposites should be carefully planned regarding the working safety, an overview of the safety equipment was provided as well as an assessment of the toxic potential of nanomaterials. Quality and well obtained preparation process can contribute to the rational utilization of the nanomaterials, and by that, it could reduce negative environmental footprints released from production as well as application of the nanomaterials. The main research findings of this paper provide useful guidelines for researchers dealing with the preparation of nano-enhanced fluids and phase change materials that should be helpful to get insights directed to the complexity of the preparation process and ensure an efficient preparation process. (c) 2020 Elsevier Ltd. All rights reserved.