A hearty heigh-ho to everything Don said...those posts are worth the price of a 1/2 hour lesson right there.
One huge frustration I have in trying to "get the right sound" from someone I admire is that I don't have the hands that other person has. John Denver, for example, is said to have had huge hands, and he frequently used his thumb for some 6th string bass notes. He could also make 5 fret stretches. No way my thumb is going to make the 6th string ring clearly, and I can hit a 5 fret stretch only if it is WAY up the fretboard. BUT, and this is something I have learned to put up with, I can make certain runs, chords and passages sound okay by altering a fingering slightly, or omitting certain strings. It is not the "original" sound, but it sure is "original" by me!
Another thing I learned...(stole the idea actually, can't remember from whom) is that stretching the webbing between your fingers REALLY helps. You can stick your fist in between each of your fingers on your fretting hand for a few seconds before you play, or use a tennis ball, or some other suitable tool that gets your fingers to spread out. It really helps. This must be done before each practice session, but I can tell a difference between when I do it and when I don't.
I actually have more grief on my 12 string than my classical, because the pressure needed to get both strings down is different - fat string and skinny string so close together. But when I switch from my 12 string back to my six string it is SO easy.