This is invaluable.

Take LOTS of pictures. You'll be surprised you thought you took a picture of that framed wall only to have missed the exact spot you need. Also take pictures of the ceiling of each room. Did I mention take more pictures then you just did? Do it.

At key points (where you may mount a TV), take a picture of a measuring tape opened across 3 joists - you'll thank me later :)

Ensure you take pictures of the garage frame and garage ceiling as well. If you are able, add extra power outside and if you're really able to, add a gas line (yes, I know gas is bad) outside too where you want a BBQ or firepit - again you'll thank me later :)