It's all about light and how you use it. Not every image has wide dynamic range that causes the camera to fill up a histogram on a capture, but when that happens compensating for it in post can make all the difference. When I saw your shot I immediately knew that you probably had a gap at the high end of your histogram - in other words, a lack of whites. When I checked, sure enough.
Your image isn't overly dark - you don't have a spike at the black end of the histogram - you just aren't fully utilizing the dynamic range in your shot. The first thing I do in post is check my levels and when I have a shot like this (where there's a gap at either end) I slide the empty endpoint to the point where it hits the light information. All your post processing controls are based around the idea that you have blacks, shadows, highlights, and whites, so when you have a histogram yours any light adjustments effectively does nothing to your "whites". This is critical because just about every adjustment (and contrast specifically) assumes you've filled the histogram and they act on each section accordingly. So without whites you're going to get dull and flat when you want pop.
Sliding the boundary does nothing more than redistributes your limited range across the entire range, and you can see the difference. Generally after this I will play with the midpoint sliding it left and right to see how that impacts the look. If you're in Photoshop you can also click the AUTO button with will set your endpoints based on the light info and then calculate a midpoint based on the rest. I find that I generally have to tweak the midpoint a little depending on the subject matter, but it gets it close. In Lightroom or Camera Raw you can hold down the Alt/Option button and slight your Black and/or White slider until the white screen you'll see gets just a bit of yellow (blacks) or red (whites) which means you've now set that endpoint correctly.
From there it's all about what you want to do with the image, but setting your levels should be the first thing you do when you get into post. It makes all the difference.