I have never styled a wig like that, so my only tips for you is to look up tutorials online. If you can't find one specifically for his hairstyle, try to find some kind of general spiking tutorial, there are lots and lots of them, I've seen plenty on youtube, deviantART and sites like that. Make sure you have a good base wig too, I've heard that the Punky ones from the cosplay.com shop are good for spiking, and I've also heard some people using the Magnum wig from Arda for characters like Roxas. But yeah my main tip; Do research, find out what kind of products to use, what kind of wig is the best and how to form spikes etc.
Also, kudos to you for cosplaying Spitfire, I'd love to see more cosplays of him, he's my fave Air Gear character~