Complex sentence: Having previously been manager of Cambridge United between January 1978 and 13 December 1983 and Brentford, his spell at Cambridge United saw the club in the Second Division where they managed respectable finishes, with eighth in 1979--80 being their highest.
Split into simpler sentences: Having previously been manager of Cambridge United between January 1978 and 13 December 1983, and Brentford. His spell at Cambridge United saw the club in the Second Division where they managed respectable finishes, with eighth in 1980 being their highest.