This video was posted on YouTube recently, featuring college pitcher Sam Demel walking us through his mental thought processes on the mound. It's promotional, for Brian Cain's Mental Training DVDs, as you'll see, but there may be some useful info here. I didn't listen to it with sound, but one the one thing stood out to me while watching it without audio is how long it takes him between pitches.
Your mental "focusing" process needs to be much quicker. Sam takes sooo long between pitches, collecting himself, that I think it actually works against him. Notice how the hitters are constantly stepping out of the box? It's tough to establish a rhythm when you take 15 or 20 seconds between pitches. Throwing strikes is about establishing a rhythm and having good mechanics. your mental process needs to compliment that -- not be at odds with that.