For example, for ordinary fluids, we have polar and apolar ones. The "rule of thumb" is that polar fluids mix with each other, and also apolar fluids mix with each other, but polar fluids don't mix with apolars.
Of course, it is not a very exact rule. For example, bensene mixes in water - but it does it badly. While the also polar ethanol mixes water very well.
What is the case with liquid metals? Does some analogous - possibly more complex - category structure exist?