Tubbs was an assistant at Lamar Tech from 1960 to 1971. Later, he was head coach at Southwestern University from 1971 to 1973. Tubbs was the assistant men's basketball coach at the University of North Texas for three seasons, 1973-74 & 1974-75 under head coach Gene Robbins and 1975-76 under head coach Bill Blakeley. In Blakeley's first season at North Texas, Tubbs, with newly hired assistant coach Jimmy Gales, helped turn around a team that had been 6-20 in 1975, to 22-4 in 1976, averaging 96 points a game – the second highest in the nation. After that season, Tubbs accepted his first head coaching job at Lamar University for the 1976-77 season.