With any graphic that I make, whether it be an avvy, profile pic, or siggy, I always do this step before I do anything else. It helps create a crisp image, clean it up, and gives you a layer to play with when you start adding gradients, textures, color fill layers, and anything else you may want to add to your graphic.
So, using the image that Ro provided us, you start off with this:
I duplicate the layer and then user the Sharpen tool. I use Adobe Photoshop Elements, so it is literally a click and drag a box from the tools menu, but you can access it from the Filter drop down menu. I do this once and then set that layer to Lighten to get this:
The difference is VERY subtle, but there. The image is more clear and the lines are more defined without making them too sharp or too rigid. A side by side comparison of the house may help you see the difference better:
When I want to lighten an image I do the same thing (sharpen) but instead of lighten I set the new sharpened layer to screen and get this:
When I want to darken the image or know that I will be working with a lot of fill layers (gradients, textures, color fill, etc) that can sometimes drown an image, I will set this new sharpened layer to soft light:
