Regarding the oboe/clarinet blend, woodwinds don't blend or sound as homogeneous as the brass or string sections. I usually use woodwinds more for color, since they get unique sounds. I find strings to be relatively the same, as well as brass. usually I get more unique sounds depending on the timbre of the instrument (most notably the higher positions on a cello). And don't forget percussion instruments as well.
Try looking up info on orchestration. I was hurting in that area, but I have discovered some tricks to combination. An easy one is using octaves for transparency (whether soft or loud) and using more saturated chords for a heavier sound.
Try this for orchestration
http://www.musique.umontreal.ca/pers...k.O/index.html
Try to look up Principles of Orchestration, as well.
Also go here
http://vsl.co.at/en/70/149/150/46.vsl
Choose an instrument, and then click on Instrument Combinations
Experimenting also works.
I'm trying to learn a lot of this before I go to college. I'm signing up for an orchestration class. If you discover anything else. Please let us all know here.