A little used system of opening leads as follows:
Against no trumps:
Ace from a strong holding (eg A-K-J-x or A-K-10-x).
King from a weaker holding. Queen from Q-J-x or a weak K-Q-x holding.
Jack from J-10, but no higher honour.
10 from an interior sequence (eg A-J-10-x or K-10-9-x).
9 from 10-9-x.
Lowest from a suit headed by an honour (but not one of the above honour combinations).
Second highest from suits without an honour.
Against a suit contract:
Lower of two touching honours.
Third and fifth from an honour or non-touching honours.
Top of nothing.