Re: Writing Symbolism
Well, perhaps take the key events you'd like to be symbolic and break them down into their component parts first of all.
In the example you use you talk of an adult vampire having turned a child into one, and reflecting on the consumption of a log in the first from the inside out.
The keys here are that vampirism is consuming, ends in ashen remains, and comes from within once afflicted.
Move on to a warewolf for example and you could say the transition from man to animal, the erosion of human reasoning and submission to base instincts could be symbolised in watching a heavily drunk man fight in the street, with disgusted onlookers around him, or a dog abused as a pup turning on its owner etc.
Hopefully it should come naturally, and not be forced or implanted. Personally I think I have a problem in too much musing by my characters and too much forced symbolism!