You're right, you generally want to keep a constant cadence and use gearing to keep it there as the wind, terrain, and your conditioning dictate. For most new cyclists, 90 rpm feels way high at first but that's about where you want to be. I think a cyclocomputer with cadence is the best way to calibrate yourself to riding with the right cadence. After a season or riding you won't need it anymore.

Picking up the pace will come with time. At this point it's more important that make it fun so you keep riding.