General Synonyms:
* Conventional
* Classic
* Established
* Customary
* Time-honored
* Age-old
* Standard
* Orthodox
* Old-fashioned
More specific synonyms:
* For customs or practices: ancestral, customary, hereditary, inherited, ritualistic
* For art or design: classic, conservative, historical, antique, vintage, retro
* For food: authentic, home-style, old-fashioned, classic
* For education: formal, rigorous, academic, structured
The best synonym for you will depend on the specific meaning you are trying to convey.