For their relationship depending on altitude, I just remember ERTM, for EAS, RAS, TAS, Mach. Draw a vertical line for the one which is constant with altitude, then draw angled lines from the same base point upwards to represent the other ones in the sequence E R T M. For example, if TAS is constant, then the Mach number will be increasing with altitude, positive gradient line, whereas EAS and RAS will be decreasing with altitude, negative gradient lines.
That's the way I was taught, and its dead simple despite the complicated explanation above (a simple diagram would help!)
cheers
PW