For minimum unsprung weight the springs should be installed with the tighter wound section up (at the top)
As for oil level, if you are not changing the oil, measure the oil level in the fork tube with the old spring installed. Usually the new springs are of a much thicker construction and will displace more fluid, thus raising the level...to much fluid will lead to possible blown seal. Just install the new spring and measure the oil level, if there is too much You can suck the oil out with a large syringe attached to a piece of plastic or rubber tubing that you mark with the correct depth for the oil to get it to the same level as with the stock spring.
