[uncle duncan]

A realistic approach would be to find a local orchestra and get permission to sit in on some rehearsals. Or at least go to some performances. That would be a good way to familiarize yourself with what the different instruments are doing. Or even find some video on Youtube or PBS or something.

Using the charts Ethan linked, you could probably approximate what an orchestra would do, but keep in mind, even if you had Danny Elfman writing your score, it's all going to come down to the actual music. If your music is compelling, it won't really matter how you score it. If it's not compelling, well... what's that old saying? "You can dress up a pig, but it's still a pig." Or is it, "You can put lipstick on a pig, but it won't turn into a bulldog."

Good luck.