^Depending on how heavy the chatter is in your head. I could only do this after I'd done yoga for a year ^...before I just couldn't meditate. Now I let all the chatter drift to the surface, and send it on it's way til I no longer have anything but my breath.
OP - you should bang amphetamine into your veins if you wanna focus... only joking.
Yoga is good for shutting the chatter up, even just deep breathing to calm down (try counting up to 4 inhaling through your nose slowly, and then again 4 exhaling - keeping the breaths the same length...do this 4-8 (just go with 8) times, then move onto 5 second breaths, 5-8 times).
Occasionally using indica herb to shut off the chatter can work, but that's not a good habit to get into. Maybe accompany that with meditation, and then just work your way up to meditation on it's own.
Depending upon what you need to concentrate on, get everything that is keeping you fidgety out the way in the day, first, then you should be able to focus.
Also if you're not using up the energy your diet provides, you might find it hard to focus, so be very active, even if it's just powerwalking everywhere.
Peace