Hey Dizzy,
What software do you have? I can give you general raw tips, but if you're using something specific, I suspect you could get tips specific to the program you're using (ie, photoshop, lightroom, aperture, etc....)
As for manual focus action shots, it's a lot of practice. The more you're familiar with your lens and quickly focusing it, the better your chances of success. A smaller aperture, higher ISO will help out. I think you can likely get away with shutter speeds of 1/125 of a second, although faster is better....just try not to go lower than that. Having a tripod with the head slightly loosened (free to move, but not flopping around) or monopod to help stablize the camera will allow you to concentrate on following the action and focusing.