Information architecture first
Map every page to a category before designing nav. Too many top-level links = unclear IA = confused users.
Mega menu when needed
Above 40 pages, mega menus are fine. Below, they're overkill. Simple horizontal nav until you outgrow it.
Search as a backup
If the nav can't surface it in 3 taps, search should. Invest in search UX on information-heavy sites.