Hey Feb, there's a posting on noses over in the Tutiorial Section, you might find what you're looking for over there.
Noses may be vastly different but they all have the same things in common, nostrils, bridge, tip, etc....it's just how you shape those things.
You said you're having trouble with the nostrils. Here's a simple explaination on how I do mine. First I carve a 'triangle shape' for the nose, draw a straight line, in pencil, down the triangle, that will help keep things in balance. Next I angle each side of the bottom of the triangle up slightly, a very slight V shape to the bottom of the nose. This will give the nostrils a slight lift, you don't want your nose straight across the bottom.
Depending on whether the nose is a 'young nose' or and 'old nose' determines how the tip goes, young, angle the tip upwards, old, reverse so the tip 'droops' downward.
For the nostils outside edge, just use a gouge that is the size and shape you want the nostrils to be. Press straight down into the outside, bottom edge of the triangle on each side, this will give you a perfect curved shape for the outside edge.
Thin the nose till the size you want, be sure to have the pencil line the highest point, everything else flows back from there. For the nostril openings, pencil in the size and shape, that makes it easier to see if the nose is exactly how you want it. I like to use a......hmmmmm, guess it's a nail punch. It's a very sharp one, like the point of a thick needle, to make the openings, then I use my Micro carver with a small ball or point to open them up further. If you don't use power carving, use a small gouge or tip of a detail knife, that's what I used before I started using a Micro carver.
Hope I haven't made this too confusing. Let me know if I can be of any further help, good luck!

Deborah
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