1. In the beginning, I spent a lot of time on the global timeline. Yes, it's kinda a dumpster fire initially, but it becomes more useful as you build up more off-instance followers. Signal-to-noise is never great, but it's a place to start.
Follow anyone who says a couple of interesting things, or who otherwise looks interesting. You'll probably unfollow a lot of them within a few weeks, but it helps improve the off-instance signal-to-noise.