First, take the pressure off yourself,
I don’t know if anyone could say what makes a “good” collector but if you’re looking for pointers:
Collect what you like, not what you or others think you should.
If it’s Lionel postwar for example, get as many books as you can and have some fun researching, no doubt at some point you’ll see or read about something you can’t live without.
Then exercise caution, don’t run out and by “junk” with property it’s location, with trains it’s condition, look for high quality examples that are original.
But most of all have fun, that’s what it’s all about, if you buy original like new trains chances are at some point down the road the investment aspect will take care of itself.