Both manga are set in the 1930's. They feature brash and witty main characters and are filled with manly battles, valiant sacrifices, and tragic moments. They also focus a bit on history, featuring nazis and other historical factions and people.
Hokuto no Ken was one of the main inspirations that made Hirohiko Araki write JoJo, that's why both series share a lot of similarities, both thematically and stylistically. First off, the art styles are quite similar. Also, they have similar elements, and are filled with manly battles, valiant sacrifices, and tragic moments.
Of all the parts found in JoJo's Bizarre Adventure, I feel Battle Tendency had the greatest emphasis on family bearing a similar tone to Ultimate Muscle aka Kinnikuman Nisei. Both contain story arcs centered on the descendants of heroic families such as the Zeppelis, the Joestars, the Robin Dynasty, & the Kinniku Clan, etc. These manga carry the spirit of manly 80's shonen with emphasis on camaraderie and multiple bizarre events throughout the story.
An earlier piece of Araki's works, the character of BT and his antics in Mashounen BT can be seen as being very similar to that of Joseph Joestar in Battle Tendency; both characters make use of trickery, deception, cleverness, and impressively immense amounts of luck to come out as the victor in the conflicts that they face.
Both manga feature main characters that find themselves caught on the opposing side of supernatural enemies of skill and power far beyond theirs and both use quick wits and brilliant tactics to defeat their monstrous adversaries. Great battles with brilliant tactical execution featured here, something most battle manga seem to lack.