Hmm good Quote; but Antiqua is best choice :P

Well, the main thing is don't go overboard. If you're doing things you need a tutorial on, you probably don't need to do them. The human eye has a tendency of skimming over things which are too complicated.

I'm going to tell you how to do it in photoshop, because I think it's the better software and I'm more skilled with it: the "enhance" menu, the undo button, and lots and lots of experimentation are your friends here. Play with the levels, contrast, color concentration... and know that if you dislike something, you can always undo it. You'll know it's good when it looks good to you. You can also play around with the blur/smudge/sharpen tool, in case things look to sharp, or to blur the edges of the photo and put emphasis on the center of it.

For the final touch, use a cool font (although not too flashy; still readable) and write the name of your project or something. This should be in blank space, not covering any important aspects of your project, and be careful that it's readable and doesn't contrast badly with the background. If you need a custom font, there's a good website called "Dafont.com". If you still want to add more, in the text menu, there should be an option which lets you add special effects to your text, I like to emboss it or something like that.

That's really all you need. If you add more, you're probably going overboard, but just use your better judgement. Also, make sure you take the best shots in game, before editing, too. Click F1 (?) to hide the GUI, and depending on the project, it might look cool to get a sunrise/sunset shot.