Buy a better camera body (like the 5d3/1dx af system) and couple it with the newest lenses that have enhanced precison vs. older L versions, that's for example the 24-70L2. Top-notch af precision is expensive (Canon makes sure of that), another reason you need a good af system is that you have to prevent focus & recompose errors by af'ing right on the spot.
Thanks for the comment regarding how to improve precision.
I used my 50L with 70D usually. Still can not AF properly. But when I use 50L on 6D, it nails focus.
Tbh, 6D does a good job doing AF. even outer points, when I feel lens af locks on, means it really is on focus on the 6D. Never miss anytime. Unless user error.
But on the 70D, I keep praticing shooting my wife, but they miss every time.
I put af on her eyes, still does not make it. I put af on her smile, it won't focus.
But it locks on object.
Maybe because there's shadow in her face, or no contrast enough, or may hand shakes, contributes to not focusing.. But what ever it is. My 6D af everytime, even face is under shadow.
Still fustrated, need to practice and test more. Both 70D and 50L already was service by canon.
Next test, I will use AF assist light from speedlite, and see results.