At the time I'm writing this, I have completed 40 marathons, 36 half marathons and many other races. Recently, I volunteered as a photographer at a small marathon. Based on this, I would start by asking a few questions:

1. What is the purpose of your photos? Do you want to show the general event, photograph a few friends, or get individual pictures of nearly all runners?
2. What kind of race is this? Road race or trails? How many runners - dozens, hundreds or thousands? Do you expect large crowds along the course? Is the course closed to traffic or do you need to plan for extraneous cars and pedestrians?

Clearly, you need different strategies for a major marathon like Boston, Chicago or New York than a small marathon with 100 runners.

Next, I looked at EXIF data from photos of me in races, and I found the following pattern:

• 70-200mm lens on a crop-frame (APS-C) body
• Shutter speed of 1/500 sec

Since nearly every marathon is in outdoor daylight, I didn’t need the speed of an f/2.8 lens, so I used a lighter 70-200/4 lens with the following camera settings:

• Continuous autofocus
• Shutter priority at 1/500 sec
• Auto ISO
• High-speed continuous shooting
• JPG, to minimize storage and card writing times
• Image stabilization enabled, to help me frame the photos
• A 64GB memory card and spare batteries!

Next, I picked course locations that were:

• Particularly scenic
• Where I could see the runners without getting in their way
• Where I could easily drive from location to location

While I waited at each location, I used a small folding chair and listened to podcasts and music - you can't read a book or a screen because you might miss the runners! As for timing, if you are just photographing your friends, ask them about their race pace. If you are photographing the larger field, ask the race director for the timing of the aid stations, which should tell you when the runners are expected along the course. Don't forget that the group of runners will spread out over the length of the course.

Afterwards, I wound up with about 5000 photos. I wanted to minimize the post-processing work and storage space on my computer. Using the thumbnails as a guide, I imported 3 of each runner and picked my favorite; if I didn’t like any of the 3, I returned to the card and imported a few more.