Well, first you need to have spokes at the right length at hand, they may not be the same for the wheels different sides. The fastest way is to cut the old spokes out all in one go, then pull the rim tape off th get the spokes out of the rim. Once you've cleared out all the old spokes you can insert the new spokes into the hub. As soom as all spokes are in place it's time to start connecting them to their right place on the rim. This can be a bit tricky, check out www.sheldonbrown for instructions.
A way slower method is to replace ths spokes one by one and interlace them as you go. It's tedious, but it gets you away from having to worry about how it's supposed to go together.