Notwithstanding all the excellent advice here, especially from my erudite and esteemed fellow aviator Chilli Monster, I quite liked the Military training rule to ab initio students which was if the runway was not clear at 200 ft solo or 100 ft dual (cos instructors know what they are doing - ahem!) then you go around. I find this useful to teach at airfields without ATSU where, as we all know, it is not permitted to land unless the previous a/c has vacated (not going to go into the definition of vacated on this thread!).
Different case though when ATC issue a "Land After" but even then it's up to the following pilot as to whether he feels it prudent to continue to a landing.