This is difficult, because it really isn't a matter of providing a succession of instructions along the lines of "rub in this spot, this hard, in this direction, for this long". Instead, in order to deliver the perfect foot rub, there are three things to get right.
Firstly, and quite importantly, you have to understand what the problem is with the foot in question, what the foot rub is intended to achieve. So therefore you need to know why your subject asked for a foot rub, or you need to have observed the feet in action, or you need to ask how things are with the feet.
Secondly, and more importantly, you have to learn enough anatomy and physiology that you understand how a foot is constructed and can address the underlying causes of the problems described earlier. So therefore you might want to study feet in general, or perhaps put some serious time into familiarising yourself with the particular feet you're most likely to be rubbing.
Thirdly, and more importantly still, you have to really want to do the foot rub well. You have to approach the foot rub with your whole attention, with your whole mind. If you're fortunate enough to find yourself working on a foot that's attached to the right person, you may find yourself in a position to approach the foot rub with your whole heart and soul too -- and then results are typically excellent. But even if not, you still need to take the whole process seriously.
Finally, a brief word about technique. If you know what the foot rub is for, and you really understand what makes a foot work, and you approach the foot rub in the right frame of mind, then you are guaranteed to deliver a good foot rub and anything I could tell you about technique is completely superfluous. So this brief word about technique seems to have turned into no words at all.