I still struggle with this. I need to do something to keep rhythm and I need a foot tap.
But…I am holding in a classical position and the guitar lift is on the left thigh and the end of the lower bout on my right. Tapping either foot bounces the dang guitar! I have tried toes only, wow, that is harder than I thought. Head bobbing may be the way to go, but there seems nothing natural about it.
I use the metronome, but I really need a physical way to match it.
My experience is that foot tapping hurts my playing just as often as it helps me, so I just let it emerge naturally. This usually happens when I really find the groove in a song I know well.
Is there something specific in your playing that you think will benefit from foot tapping?
If not, I wouldn’t worry about it. In fact, I vaguely remember reading that classical teachers discourage students from tapping their feet…though I can’t remember why.