Well there is to much to say and I don't think there would be anyone patient enough to explain it all to you, so I would say the best thing for you to do is find themes that have the effects you want, for example there was a heavy rain theme here I think a while ago and then extract them using Patpat's GUI_CTF_tool and then extract the rco's using Rcomage and see what commands and stuff they've used in the xml and for the images you use for the icons and other stuff try converting the image mode from RGB to Index color with a very low color maybe around 40 or 50 I think would be enough. (as long as your Icon doesn't loose to much color lower it as much as you can)