How do I put sprinkles, nuts, crumbs, etc. onto the side of a cake?
When I've done this (on a fondant covered cake), I've brushed a thin coat of piping gel over the entire surface, then used my cupped palm filled with sanding sugar (or whatever) and pressed it onto the cake. I've never had a problem with it not sticking. I've never tried it with nuts, though.
If you are doing it with an iced cake, do the cupped hand technique before the icing crust.