1. Spend half the film reminding you what happened the first time round.
2. Spend the other half lecturing the audience on demonic possession and olde time-y history; this should purely be done expositionally.
3. Fail to establish characters the audience can empathise with, so no pointless foreign nannys like in PA 2.
4. LESS IS MORE: this is probably the most important thing, the reason why the first one works so well is that there is only one camera. In the 2nd one, there’s a whole fucking army of them recording every room constantly. What the audience percieve to be happening can often be the most frightening thing (Alien & Halloween being prime examples of this).
5. The amount of footage should be realistic too. In the first one, they filmed for several hours each night – this is fine. In the second, 6 high definition cameras are filming ALL THE TIME. Imagine the size of their hard drive.