Use search fonction there is tons of valuable information in the forum already
Long to short example (start by doing long run with equal times on both)
w1 2x300m 7 min recovery
w2 2x300m 10min recovery
w3 2x300m 12min recovery
w9 200 / 150m 30min recovery
Short to Long
w1 4x3x60m (3R;7S)
progress with that over time then use some SE
80-100-120-150
SPEED ENDURANCE 80-150m
SPECIAL ENDURANCE1 150-300m
SPECIAL ENDURANCE 2 300-600m