THe level and feedback settings are going to vary depending on whether you run it in front of the amp, or in an effects loop. The more dirt/compression after the delay, the lower you'll want to run them.
I have my DD-3 in front of my Marshall 18 Watter clone (dialed in moderately crunchy) and I run the level and feedback at about 9 o'clock, with the delay time at noon (longest switch setting). Works for Police and some U2, but that delay's kinda long. FOr more genreal use, you might want the delay around 10-11 o'clock.