Originally Posted by Velo Dog

Way too much thinking here. You never, ever need to think, "I'm in the 2-3" or "I'll shift to the 1-7." If you move a lever and things get worse, move it the other way. You'll get the hang of it in a few rides.
As an exercise, put the chain on the middle ring in front (small ring if it's a double) and go for a ride shifting only the rear. Forget the front exists. When you master the rear, in about six minutes, then you can fool with the front. Those numbers are useless, though.