My mobile phase for HPLC (High Performance Liquid Chromatography) test consists of 3 components in the ratio 5:250:745. In preparing the mobile phase, is it advisable to first measure 745ml of component A, followed by 250ml of component B and lastly 5ml of component C?

First, you should know that I've never done any HPLC work; however, I know, in general, how it works.

I assume all three of the components are miscible. Furthermore, I assume you will mix the three components together. In view of these assumptions, I don't think it makes any difference in which order the three solvents are mixed.