I use Nikwax cleans your boots and keeps them waterproof
After using Nikwax for years I think it's total crap. It completely dries the leather of boots which causes fractures that eventually lead to holes in the leather. This is how my LaSportivas ended up after one year:
I haven't found an alternative yet, but I've been experimenting.
Here's a description of how I impregnated my boots, but it's in Polish so you either have to use google translate or just let the pictures speak for themselves. As I said, this is an experiment, I don't know yet if I can consider it a success but so far everything looks fine.
EDIT:
Here's another description of impregnation - these are not mine.