Why aren't my photos crisp and sharp?

While I feel I'm a fairly competent photographer, there is still many things for me to learn. My DSLR is packed full of settings that I still don't fully understand.

One thing that has been bugging me lately, is that I can't always achieve the focus/sharpness I want out of my photos. Because of my desire for tack sharp images, my 50mm 1.4 lens is my favourite. But even using that, I don't always get it right.

I found a really good article that explains things to do with focus and sharpness. For example better techniques in using auto focus - how the orientation of the focus points can actually affect how it works. And what the hell does "One Shot" and "AI Servo" mean? One is for stationary objects and the other is for moving objects! I feel much better informed now and will have to try playing with these new found settings.

http://photo.tutsplus.com/tutorials/shooting/achieving-better-focus-and-sharpness-in-your-images/