Well, a good start would be to turn the sound off…
Seriously though:
1. convert the the footage to black and white
2. apply Levels and blow the highlights/mids out while increasing the blacks. Old film was poorly made and required very strong lights to expose. Therefore, everything looked more blown out and contrasty.
3. create a black solid. create a circlular-shaped mask that touches each edge of the frame. feather it out heavily and invert it. Turn the opacity of this layer down to something like 10-20% and you’ve got an easy vignetting effect.
4. introduce that subtle flickering effect by keyframing the opacity of the footage between 100% and something like 97% fairly rapidly.
5. Add very mild grain using After Effect’s grain tools
6. DON’T do things like simulated scratches, they are almost always a dead giveaway that it’s a fake.