All the story missions.
You also need to do the bonus mission which are:
Vigilante Missions, Paramedic Missions, Pimping missions, trucking missions, taxi driver, firefighter missions, burglary missions, driving school, pilot school, bike school, boat school, 8-track, blood bowl, kickstart, the gyms, chiliad challenge, shooting range, dirt track, bmx challenge, lowrider challenge, valet parking, courier challenges, nrg-500 challenge, import/export, fright train, quarry missions, & checkpoint challenges.
You also need to buy all properties.
Also, 100 graffiti tags, 50 horseshoes, 50 photo ops, & 50 oysters.