1
general::
Making a good start, progressing well, as in After the first episode the new soap opera was off and running. Originating in horse racing, as the traditional announcement at the beginning of a race ("They're off and running"), this phrase began to be used more broadly in the second half of the 1900s.
American Heritage Idioms
2
general::
Phrase(s): off and running
1. Lit. [of horses, dogs, or people] having started racing. • It’s a beautiful day at the races, and, yes, they’re off and running! 2. Fig. started up and going. • The car was finally loaded by 9:30, and we were off and running. • The construction of the building was going to take two years, but we were off and running, and it appeared we would finish on schedule.
McGrawhill's American Idioms And Phrasal Verbs