I defer to those who went before on the use of filters...but if you want to/have to give it a go in post-processing, here are a few things to try:
1. Judicious increases in global contrast and saturation can help.
2. Local contrast enhancement helps too -- there are a few ways to do it, but the easiest is to use unsharp mask (lots of tutorials out there -- here's
one).
3. If your software supports layers and blending modes, then doing a duplicate layer and blending down on multiply can work wonders -- you can use the opacity slider to fine tune the effect. There is a variation on this, which some people call the Orton Effect, which involves blurring your duplicate layer a bit first, thereby creating a bit of a glow around your subject).
4. If your software supports decomposing into LAB space, then you can try this
trick, which I find works really well. Don't worry, you don't actually have to understand what LAB space is to make it work. .
5. You can also use the Channel Mixer, like
so.
You can also tweak the individual channels in levels and curves, but I have not had a lot of success with those approaches -- requires too much skill maybe. Here's a
tutorial from a photographer who seems to have mastered this technique.
Good luck,
EL