Run numbers. Do simulations. Have a plan.

I concentrated too much on minimizing long-term interest expense. I didn't think about how the money I was using to pay-down principal could have returned income over the long term. The real estate asset I was paying on hasn't appreciated at all in 20 years. I could have seen major investment returns on that money which would far exceed the interest expense I alleviated.

re: investment, one reasonable place to start might be Bernstein's free ebook "if you can", which also has some pointers to further reading. some of the advice in there, re: tax-advantaged retirement savings plan, is specific to the USA

http://efficientfrontier.com/ef/0adhoc/2books.htm

The bogleheads community is really good for advice on just about any financial topic you can think of. Tell them your situation and they will set up a solid plan for you https://www.bogleheads.org/