BMXTRIX covered most of the points I would share. Spot on about the garage, BBQ/deck, and other "outside" areas as well as the wire gauge.
A few comments to add, from my experience with our home build and basement finishing project:
- run conduits through hard-to-access areas which would be a pain to add wire to later (tight crawls, attic spaces). Some come with fish line, which makes it a cinch to pull a bundle through later. I added a
front-to-back-of-room empty conduit on our basement theater build, "just in case".
- as BMXTRIX stated if the walls are open, run wire to wherever you think you might want it later. All AV components and TVs now support network-connected setups, so think on that ahead of time. Lighting setups can also require prewire/conduit runs just like audio.
- We went with Sonos in our basement remodel, which may not be as popular on this forum as the hand-selected component setups. But it's dead-simple to use, particular with all the streaming sources nowadays. I put 4 8-inch ceiling speakers in our home gym and one of the network-connected Sonos amps, and it made setup a snap.
- think about where you want TVs vs just home audio, say for example you want to wall-mount a TV, and switch between TV and overhead or in-wall speakers
Best of luck with your project!