There's the strength leaderboard and the prestige leaderboard. Prestige leaderboard can be achieved by winning wars, and gaining prestige from doing so. Strength leaderboard can be achieved by having strong members, basically. The same things that make players strong, eg; allies, stats etc... If your whole clan has extremely strong players, then you will most likely be on the strength leaderboard.
Uh, if each of your members has lots of pieces of equipment, that may help, though im not to sure on that one.
If you have over 65 HLBC members in your clan, all above max ally plunder, then you will most probably be on the strength leaderboard.
For individual ranking in the clan, I believe stats and bfa are the major factors that are used. That's why you can see many people with a lower lb ranking but higher in clan ranking than their clan mates. Also remember that spy stats are weighted heavier than attack stats when it comes to ranking
Stats, perm items, allies, battles, value, spy's victories (assassinate, Steal, scout) are all figured in