If your chocolate does start to burn and go grainy you can add a few drops of vegtable oil to bring the chocolate back to a useable consistency.
You can melt the chocolate in the microwave however melting over a pan is much better to keep an eye on.
If you have a steady hand and are confident you can do the design straight onto your food providing it has a flat surface.
The webs are delicate so if making treats that need to be taken out of the house it might be a good idea if having them stood up to not add them to your food until you are where you are serving them.
If you have very hot hands, try cooling them in ice water before handling the webs as they melt very easily.
If adding webs on top of ganache you place them on when the ganache is still a little warm, this melts the webs slighly to get an extra clean look and lines.