One of my favourite quotes from Spurgeon is on the appropriate length of sermons. I was sure it was in Lectures to My Students, but somehow it managed to evade all my attempts to find it. But I eventually located it in Lecture IX “Attention”:

A man with a great deal of well-prepared matter will probably not exceed forty minutes; when he has less to say he will go on for fifty minutes, and when he has absolutely nothing he will need an hour to say it in

 

Spurgeon has a lot of great stuff to say in the lectures about not being boring as well. Another of my favourite quotes:

‘Watch and pray,’ says the text, ‘Go to sleep,’ says the sermon.”