Setup will vary from rider to rider, depending on weight and type of riding they do. A good place to start would be to download the owner's manual from Polaris and read through the suspension set-up procedures so you can get a good baseline.
And remember, the owner's manual assumes springs and shocks are new or that the sled has been well-maintained. So make sure the pre-season maintenance has been done and your shocks and springs are serviceable.
Here's a link to the Polaris website and the 2005 manual.