Unfortunately, this is one of those problems that just takes practice and concentration work. Actually the memory game can help with this, and you can use two sets of runes or two weeded tarot decks with this. Yes, also you might want to try a shamanic journey using repetitive sounds either drumming, rattles or something similar to focus your mind. I find that people who have a hard time ''turning off'' do better with the shamanic work.
I'd recommend Michael Harner's cd's... he has an entire series dedicated to it. I have to admit, I've had the best luck with live drums, but a cd does work, too.
If you are looking for some kind of system to help with this kind of focus, Christopher Penczak's book ''The Inner Temple of WitchCraft'' (book one) or ''The Temple of Shamanic WitchCraft'' (book three). Silva has a paperback book which has an entire series on mind control, but I tend to pick and choose. The beginner excursuses in particular are useful for the problems you seem to be having. (to find this, look up Silva Mind Control in a search at Amazon.com under used books. I have no idea if this is still in print. ) Also, Kerr Chuluhain in ''The Wiccan Warrior'' also has some good suggestions.
Also, Aden McCoy in ''Making Magick'' also has good ideas for this.