Mint takes an age to boot

[Deadly Ferret]

I have a machine which is dual boot Linux Mint and Windows 10, on a solid state disk. Initially both started very quickly, though Windows always had an edge. Now though, a year or two later, Mint takes about a minute to reach the start-up screen. (Windows takes less than ten seconds.)

Any ideas on simple checks I can make to diagnose/try to reduce the start-up time please?