Dog photography

A friend's dog has been diagnosed with cancer and does not have long to live.  She's asked me to take some photos of him whilst he can still run around.  My problem is that I've only ever photographed landscapes and buildings and I haven't a clue how to approach (fairly) fast action photography.  I'll be grateful if someone can spare the time to give me an idiot-level guide to the settings and approaches I'll need to use.

I have a D300S, 17-55, 70-210 and (if needed) an SB800.

Thanks in advance.

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Best wishes,
Alan J