Friend of mine back-tested the simple "the next king is the first son of the previous king" against the past 1,000 years of English kings and found it to be true only half the time.
I did the same - taking only the kings/queens of England (i.e. starting with Alfred and ending with Queen Anne, ignoring those after the unification of the United Kingdom).
Son is by far the most common (21 from 50), followed by brother (6 from 50).
The next two are especially interesting - 5 new monarchs were usurpers (i.e. not closely related to the previous monach) and 3 times the new monarch was also an old monarch (i.e. a previous King was returned to the throne!).
There were 4 or 5 female successions (twice a daughter, twice a sister and once a daughter-but-disputed-succession [i.e. Matilda]).
Only once does it looks like the succession totally jumped a generation, and a grandson succeeded. In every other situation it looks like people were in the same generation (i.e. brother, sisters, cousins) or one lower (sons, daughters, nephews).
And only once did the succession 'jump back' a generation, with Richard III succeeding his nephew.
I was really hoping that Charles would just be king for a day and give it to William thereafter. Get some fresh blood in there, as well as a figure that didn't have 50 years of somewhat controversial behavior lined up behind them.
Friend of mine back-tested the simple "the next king is the first son of the previous king" against the past 1,000 years of English kings and found it to be true only half the time.