Make it sound as realistic as possible. I start with a few grunt calls...usually a mature and then a young buck grunt. Sometimes (when I feel deer may be close) I only rattle for a few seconds, other times I do it blindly for 30 seconds or more.

If you've witnessed bucks fight, it's a lot easier to rattle. Sometimes they last for 3 seconds...other times they go on for several minutes (with slight breaks). They make a lot of noise kicking dirt and leaves around...and also tend to grunt often before, during, and after the fight.