Ever noticed that photos on some websites really has nice vibrant colours (no I didn't spell colours wrong, this is how we spell it Downunder - I digress) that seem to really catch your attention? Yet, your photo's are somewhat muted and dull in comparison.
With a very simple technique in the GIMP you will have your photos looking great in no time. Just one thing that I will say at this point is that you can make a good photo better but you can't make a poor photo good. So, before you start thinking I can fix all those duds, that's not what this tip is all about. This is about taking an already good image and improving it.
Figure 2: After (opacity 35%)
Figure 3: Over processed (opacity 90%)
Tip: Don't overdo things using this technique. Whilst not easy to see on these small images, Figure 3 is far too saturated and looks unnatural.