Don't make yourself crazy thinking in terms of gear numbers, or even gear inches. The poster who mentioned not crossing your chain is right. It's hard on the drivetrain and it's less efficient. Here's what to do: find a cadence that's comfortable. For most riders, around 80 to 85 rpms is pretty good. A lot of newB riders mash gears that are way too high. Think about it: is it easier to lift five pounds 20 times or 100 pounds once? High rpms=good. Once you are moving at a natural cadence, shift as effort demands. Try to keep a steady cadence. Whacking big hill or killer headwind means you probably want to drop into the small chainring. Use the rear end to fine tune.

Happy trails,
Mark