Hmm, I don't think it's in the scope of the project to tell you where to place the markers, it really depends on what you want to study. This should normally be based on the specific domain's literature.
Placing markers in one place or another doesn't really change how they are tracked inside the software, the only caveat is to be aware that cloth or even the skin can "swim" a bit above the actual point you want to track, and that occlusions are not well handled so you may have to manually correct the track position during the frames they are occluded.
