The present research aims to suggest a three-step guideline towards selecting a proper Nanofluid regarding the heat transfer effectiveness. To do so, employing two-step technique, the nanofluid's samples were prepared in various nanoparticles' concentrations (0.125, 0.25, 0.5, 0.75, and 1%) of MWCNT-ZnO hybrid nanoparticle in a thermal oil. The samples' stability has been examined employing the Zeta potential analysis. The samples' thermal conductivity has been experimentally measured at various temperatures (15, 25, 35, 45, and 55 degrees C) and solid concentrations. After that, a three-step guideline to select a proper nanofluid as a heat transfer fluid has been proposed. Then, for both the internal laminar and turbulent regimes, variations of pumping power due to adding hybrid nanoparticle has been theoretically studied. Furthermore, the possible effects of adding nano particles on the convective heat transfer coefficient in a microchannel heat sink have been investigated. The results declared that the convective heat transfer coefficient had been enhanced by 42%. It is concluded that the produced nanofluid, as coolant fluid, would bring a certain benefit in heat transfer applications. These pre-assessment process would ease the decision-making process in selecting a new coolant which possesses superior heat transfer properties in comparison to the conventional coolants (Le., water and oil).