If you run a modern computer, chances are high that you have a multi-core processor. That forces us into paralell programming to get more performance, which is much harder than doing serial programming.
The operating system and existing shell commands can do much for us, though. Let's say you have a bunch of files where each should be processed by a command. Of course, with multiple cores, this could be sped up by running multiple instances of the command simultaneously. And there's a very easy way to do that - xargs. An example for converting raw files into jpeg:
find . -type f -name '\*.CR2' \|xargs -n 1 -P 3 ~/bin/raw2jpeg
This will find all files named *.CR2 and feed that list to xargs, which will run up to three (-P 3) processes simultaneously, giving each command one filename (-n 1) on its commandline.