I figured it would be nice to share some tips and advice, things we can do after the photos have been taken and which can improve our photos before we share them with the world  If your tip is software specific, please mention which software and if needed, step by step how you do it 

My tip: If you're scaling down your image by quite a lot (for use on the web for example), let's say you're making is about half the size (dimensions), apply a sharpening filter after your resized your photo. Personally, I use Unsharp Mask Filter in Photoshop - it has options so it's best to see how they affect your photo (you can use the Preview checkbox to see the difference by just turning it on and off) but as a rule of thumb, I keep the Threshold and Radius low and apply Amount about 50% for a photo that was scaled down from 3500 pixels longest side to 1000 pixels.  Nice and crisp photos 

I've got one I use for brightening photos I've taken in poor light. I used to play with the brightness/contrast settings, but that generally makes pictures look really washed out. Now what I do is in Photoshop, I make a new layer over my image, fill it with either white or a very pale pastel colour (this is actually a good way to do a bit of colour-correction at the same time), and then set the layer mode to Soft Light or Overlay, and play with the opacity. Usually 25-45% opacity brightens up the image a fair bit without making it look too washed out.

Sometimes after that I will adjust the Levels of the source image layer, to bring the contrast up a bit more.

I will also echo Inga's tip about Unsharp Mask, it's so much better and more precise than the default Sharpen filter.

I do that too!    It's also a great way to do partial lightening up, like let's say the pinky face is in shadow (backlit photo for example), you can select the face (maybe hair too, depends), feather it a good amount and fill with white on a new layer, overlay and usually all you need is about 12% and no one would know! 

Yeah :D

Actually, I did it that way in this photo. Sacchin was overly brightly lit already (STARE INTO THE LIGHT..) but Maki was -way- dark, so I put the lightening layer over her, but not over Sacchin, and it sort of equalized them, a bit. I left Maki a bit darker though, since I sort of liked the contrast.

http://farm1.static.flickr.com/217/474928534_272eb009d3.jpg

Wow... Thanks for the tips you guys... I really need to get a new camera, but until then, I was trying to find ways to perk up my photos a little... The overlay thing is a really great idea, and I'm not sure why I didn't remember it - I was using it for school....  Well, I hope my next photos will be better~

For brightening/contrast what I do is:
- duplicate the background layer (which in this case is your photo)
- set the new layer to "Soft Light", play with the opacity to determine how contrasting you want the colors to be
- Ctrl + E to merge the layers
- duplicate the layer again
- set the layer to "Screen", play with the opactiy to determine the brightness you want
- merge the layers

sometimes I do the Screen first before Soft Light. It depends on the contrast-brightness level of the photo before post-processing.

Healing brush works great in removing stains, chips and dents on pinkys.