Jon Gosselin -- Spinning For One During DJ Gig (VIDEO)

Jon Gosselin learned lesson #1 about show biz Saturday ... Everyone's gotta start somewhere.

That somewhere was a New Jersey bowling alley, where Jon made a guest appearance as a DJ.

The good news ... the one person who got up and danced really liked it.

Truth be told ... we spotted 2 others in the background at Brewster's Bar and Grill inside Laurel Lanes, where Jon put on a 5-hour set filled with every type of genre ... the musical equivalent of throwing darts.