How do you get crystal clear water?

[goldie]

I have seen so may pictures of people's tanks and the water always looks so crystal clear. My tank always seems to have small particles floating around and on the rocks. I have had other tanks in the past that weren't as bad as this but never had pristine water. How to you all do it? I have a RSM 250. It has been running for about 6 months. I am running the stock skimmer and I do 10-15% water changes every other week.