How much information should I include in my lecture slides?
Here's a general guideline:

Figure out whether you want the audience to pay attention to you, or to the slide

They can't do both. A large part of the time, you want the audience to pay attention to you and the words you're saying. At those times, the slides should be as sparse as you can make them. Really, the only function they have is as a reminder to people whose attention has momentarily lapsed: this is what I'm talking about, this is where I am in the line of the story. Also make sure, during these moments that you're not looking at the slides. The audience looks where you look, unless you make eye contact with them.

But sometimes, you want the audience to focus on something in particular. Perhaps you're taking them through steps in a proof or derivation, perhaps you're explaining a complicated diagram, you may even be reading out a quote. These are the rare moments when you're asking the audience to really focus, and raise their energy levels for a moment. Here, you're allowed to have dense slides. These are also the slides that you're spending a lot of time on, so make sure to put the effort in. Use all the visual tools at your disposal to make the message as clear as possible. At this point, you're actually allowed to look at your own slide, because you want the audience to do the same thing.

Finally, do not mistake slides for learning aids. If you want to give students something to help when they're studying, create a version with added notes and put that online. Don't clutter up your slides to make them serve two purposes.