One of the main reasons why we can't rely on just basic drills and form practice is that we need to develop quick reflexes. I invented this method back in my Shotokan days to help me develop my blocks.
What you see in the photo are two favourite rubber balls. I use only one of them at a time. It already helps a lot if you bounce the ball against a smooth wall and catch it. What I have done to help me with my blocks however is to intercept the ball on its way back with in inward slapping block combined with a grab to catch it. Outward blocks can't be done in this exercise with much success, but I also intercept the ball with an outward circling movement at times before I catch it.
The better you get at this the harder you can throw the ball to get more speed.
I also catch the ball with my eyes closed at times, but the success rate in that is far less than 100%.
The effect this exercise has on your actual sparring is almost immediately visible- plus: you become able of rescuing a teacup or two when you least expect it...