For this cake that had gumpaste branches and red berries on it, I used a mold to give the branches realistic bumps where the buds would be. The difficult part is getting them thin enough that they don't look too ragged, but also making sure they're not too thin, or they'll break easily.
Press the gumpaste into the mold and make sure it's getting into the buds. Use a spatula or another tool if the gumpaste is sticking to your fingers.
De-mold the gumpaste and press the edges that might have been left at the back of the branch so that they curve toward the back and aren't as obvious. You can also cut them off with an exacto knife, but I prefer to just curve them around so that the branch is a little thicker than it would be otherwise.
Brush the branch LIGHTLY with brown petal dust. If you put too much on it will look too heavy when it's dried. If you want to do a dark brown color it would be better to paint it on, and also make sure that the edges from the back of the branch are cut off.
If the edges aren't cut off they won't be very obvious if you've only dusted the branch lightly. I don't know why, it just works that way. When you put them on the cake they just look like a variation of the brown color, and as long as they're not too big they'll look fine. The color should really just be on the very top of the molded piece and not extend down around the sides.
And that's your little branch. To do branches that have more than one stick and are shaped like a "Y" you can attach two sticks together, but make sure that you really attach them well. Using melted candy clay works well as glue. Do NOT use gum glue, because that can dissolve the stick since they're so thin.
Kara Buntin owns A Cake To Remember LLC, custom wedding cakes in Richmond VA