I am an Occam's Razor type of guy i.e., keep things simple. I don't think that most of those that read this or hillfit.com are elite athletes with lots of time to spend on training.
Most of us have jobs and other interests and we need to fit our training into and around our lives.
There are a few ideas here for athletes, but I actually prefer to do a couple of simpler things:
Stand on one leg when taking a p*ss or brushing your teeth.
You do this everyday, several times. When you remember, do it stood on one leg. It will challenge you balance, will not take any time out of your day and the worse that will happen is that you will get tooth paste (or urine) down your front!
Putting your socks on
When you put your socks on in the morning, do not sit down to do it. Stand on one leg at a time and put your socks on while balancing on one leg. This is a bit more intense and advanced and involves more balance and movement in the three planes.