So just kinda go by ear? (or legs, in this case!)

Did you mean higher? Gears 4, 5, 6 would be higher gears than 3, 2, 1. On flat ground, you'd usually ride somewhere in the middle. When you see a hill coming, prepare to down-shift to a lower gear as you get to it, making it easier to climb the hill. When you get to the top and level out (or start going back down) then you can shift back up to a higher gear. The idea is to maintain your cadence (the rhythm of turning the crank) so that you're not spinning too much (pedaling too fast all the time) or too hard, but somewhere in between, as much as possible.
Yes, I meant higher. I knew that. I know I did.