"Not thinking about other things than money."
is the same as 'thinking only of money.'
Not just having some thoughts about money, but thinking exclusively about money is the key idea.
MDHunter has analysed the sentence correctly and shows genuine humanity by hoping the author meant to say:
'It's important to avoid' [thinking only of money]
I'm more cynical; I think there are people who think and talk and even sing:
Money, money, money, money....
and if any one tried to stop you thinking about only money, these people might easily tell you to be resolute by saying "It's never important to do anything else":
It's never important to avoid not thinking about other things than money.