Question: I've noticed a lot of my pictures look muddy. They don't have very high contrast. I know I can post process some pictures, but what is the secret to having nice contrast in a picture?![alt text](https://i.stack.imgur.com/aDZWC.jpg)

Answer: 
Based on the photograph you posted, there actually is quite a bit of contrast. In general, I think the photo is pretty good, if a bit soft (from a lighting standpoint.) You noted that you shot the photo without flash on an overcast day, which is the primary reason for lack of any defining shadows or "lighting contrast", if you will. 

I would recommend using additional lighting if your primary light is very diffuse (like an overcast sky.) Perhaps and off-axis flash or something. A strong enough light that comes from an angle to create shadows and bring out depth in your subject.

Another word about contrast...it is not entirely tonal. Color also brings its own contrast, in a more complex form. With monochrome, you only have different levels of brightness to create contrast. With color, different colors of the same tone can also create contrast. Complementary colors, primaries, secondaries, split complements, etc. can all create varying forms of contrast in a scene, even if they are the same brightness level.

If you intend to shoot monochromatic photos, you will be lacking the element of color contrast, and will need to find ways to enhance tonal contrast. In diffuse lighting, this can be difficult, and sometimes you just need to resort to handling it in post-process. A technique that can probably be very helpful without actually overdoing any contrast adjustments is "[local contrast enhancement](http://www.cambridgeincolour.com/tutorials/local-contrast-enhancement.htm)". This is a technique that aims to improve contrast where it is necessary in smaller areas, without affecting what may be very good contrast from an overall scene standpoint. 

Here is a copy of your image with some local contrast enhancement, using Unsharp Mask @ Amount 18%, Radius 97, Threshold 0. The left half is the original, the right half has local contrast enhancement, for comparison:

![alt text](https://i.stack.imgur.com/NYST6.jpg)
* Are you using flash? Pictures with harsh flash tend have a washed out look, with dark harsh shadows.
* In my experience non-SLRs (Point and Shoot / pocket cameras) get terrible results in-doors without a flash, even in situations that seem well lit to the human eye. Photos may look waxy from too much noise reduction (which is necessary in low light to get a steady shot, hand-held).
* A lot of the time the secret is to have good lighting in the first place. Sometimes a subject just won't look good no matter how good your camera is or how you set your camera settings, if the lighting is too harsh and shadowy. This can also happen in bright daylight, for example. The shadows show up black and the bright parts overexpose--- the camera may not be able to handle the dynamic range.