finding the right focus point

[roberthans]

Often on my live viewer screen on my 100D I feel like the focus is right (doing it manual), but then when viewing it on the big screen of my computer, I notice it is just too far back or too close, basically ruining what else could be a good shot.

Now, I want to do more people photography, with a focus good on the eyes. How do you do the focus there? automatic focus or do you have a trick to do it in manual?

I didn't find the right solution from the internet.
References:
- http://www.thephotoforum.com/threads/finding-the-right-focus-point.412820/
- Professional Infographic Video Cost

please help.
Thanks.