This is what I have used for years without a single failure:
If you want to guarantee that this will work for the long term, run conduit.
If this is new construction... run conduit.
If you remember when HDMI didn't exist... run conduit.
Oh screw it...
1.25" or larger orange (or blue) conduit from Carlon is recommended. It is flexible and provides a pathway to add more cables later, quite easily, behind drywall. Do not run the HDMI in the conduit at this time.
If you have easy retro access, forget what I said, you don't need to run conduit since you can add/remove cables later easily.
It is strongly (!!!) recommended that you run several pieces of cat6 cable to the projector location as well. This will give you future video, Ethernet, and/or control capabilities as necessary.
If you haven't discussed it yet, in-ceiling speakers are a bad idea, and a long discussion of the theater space itself is worth having unless this is the tenth home theater you've put together. Builders tend to be clueless about all of this.