I prefer to teach:

Tenuto: 100% of rhythmic value
Staccato: 50% of rhythmic value
Tenuto/Staccato: 75% rhythmic value (lifted length)

Accent: emphasize the attack without shortening body of sound

Marcato: staccato + accent (emphasize the attack and abbreviate the body of sound by 50%)

My aim is to instill a COMMON BELIEF in the ensemble so that as we play our music, we interpret the marking exactly the same way.

(emphasize = more air)