Making good looking pictures in SL can be a hassle. Even do a large factor of how your pictures will look depends on your graphic settings there is a simple trick to make your pictures look a lot better.
The above picture is taken on low/medium graphics with the environment set to Midday.
The picture bellow is taken on the same graphics settings with a custom environment. There is no fancy photo editing here. The only difference in the two pictures is the light.
As you can see there is a huge difference between the two pictures. And if i may say so, the second pictures looks way better then the first.
Depending on what you are making a picture of you may want to use different environment settings. A little difference in light can do a lot.
There are a whole bunch of per-made environments on marketplace and you can also make your own under World/Environment/Personal Lighting (in your viewer).
If you like it to be as simple as possible (as me) there is the Easy Environment HUD that lets easily change your environment, add more environments and it includes the environments that i use for my pictures.