If you've looked into running at all, you already know that shoes are the single most important item you can own as a runner. Easy, right? You have a pair of cross-trainers buried somewhere from that foray into whichever sport(s) you've tried. All you have to do now, is dig them out. WRONG. Over time, the materials used to make shoes start to degrade. No, it won't be like the half-eaten apple you lost for a few weeks in sixth grade. You probably won't even be able to see a difference, but you'll feel it in your feet.
Ok fine, so new shoes then. Hit the clearance rack, grab the first pair that fit, and we can get this thing rolling. Wrong, again. It turns out that there are several different types of running shoes based on your feet and running style. First off, make sure that they are actually running shoes. Not basketball shoes, not cross-trainers, and not walking shoes.
There are a couple of different ways to determine your foot type and stride. The easiest way is to find a running store. Yep, they have whole stores for running. Crazy, right? I mean, how the hell do they get away with a whole store for running stuff?! Anyway, back to your feet. Once you locate a running store, chances are that they offer free foot analyses. Depending on the place, this could be a laser scan of your foot, measuring, watching you walk/run, or something else entirely. At my local running store for example, they have a treadmill with a video camera trained on your feet. Each member of the staff is trained to go over this video to look for foot strike, pronation, and other mysterious things. The result of this analysis will be knowing exactly what kind of foot type you have, and therefore what kind of shoe you'll need. To find a store near you, start here: http://www.runnersworld.com/store/search/1,7978,s6-240-417-0-0,00.html
If you don't have a running store near you, or don't want to go to one, there is an at-home version. Less precise, but its a start. You'll need, a tub of water (bath tub, plastic tub, whatever, as long as your foot fits in it) and a brown paper shopping bag. Cut the sides of the bag so that the bag will lay out 3-4 feet or so. Dip your feet in the water, and walk across the paper with as normal a stride as you can manage. Now, look at the prints.
The type of arch you have is closely related to your pronation (a big fancy word for how much your feet roll to the inside when you walk or run). Like everything else, moderation is key. Too much, or too little pronation causes injuries. If you have a neutral arch, you likely pronate a little bit, so you'll want to look for a stability shoe. If you have a high arch, you likely don't pronate enough, so you want a neutral cushioning shoe - one that has little arch support, and will encourage pronation. If you have a flat arch, there's a little more information needed. If there is a clear curve inward at the arch, you'll likely need a stability shoe. If it looks straighter, or even curves out from your foot, you'll need to go all the way to a motion-control shoe.
A couple of other miscellaneous tips. Running shoes DO NOT need breaking in. That thought that goes through your head that goes something like this, "Hmm, they're pretty good, maybe a little tight in the heel, but they just need a little breaking in and then they'll be fine..." Nope, that doesn't fly. If they don't fit right in the store, they never will.
On the date of your first run (or run/walk), write the date on the inside edge of the sole of your new shoes. Later, this will help you to know when its time for new shoes. Running shoes will need replacing earlier than you're used to. In general, you'll want to replace them about every 500 miles or so. As soon as your feet seem to be getting more tired than usual on a run you've done before, your shins start to ache, or if your hips or back start to hurt, and its been about that long, start looking for new shoes. Keep in mind, this will be aches and pains that are unusual. There will be usual pain, after a while you'll get to know the difference.
Update April 2017: The majority of this is still true. The only thing I would add is that I know longer write the date on the sole of my shoe. There are apps for that! If you use any kind of fitness app or wearable, there is likely a section for tracking your gear usage.Most activity trackers even do it automatically as long as you tell it which shoe you were wearing for a particular activity.
Also, the 500 mile rule is not so absolute. Firstly, the miles count during any activity. So for example, if I stop by the grocery store on my way home from a run, that distance counts even though I'm not running. In addition to that, the 500 mile rule is a guideline for the 'average runner'. What in the holy hell is an average runner?! If you weigh more than an 'average runner', you put more stress on your shoes, so your mileage on your shoes will be shorter.
Update April 2017: The majority of this is still true. The only thing I would add is that I know longer write the date on the sole of my shoe. There are apps for that! If you use any kind of fitness app or wearable, there is likely a section for tracking your gear usage.Most activity trackers even do it automatically as long as you tell it which shoe you were wearing for a particular activity.
Also, the 500 mile rule is not so absolute. Firstly, the miles count during any activity. So for example, if I stop by the grocery store on my way home from a run, that distance counts even though I'm not running. In addition to that, the 500 mile rule is a guideline for the 'average runner'. What in the holy hell is an average runner?! If you weigh more than an 'average runner', you put more stress on your shoes, so your mileage on your shoes will be shorter.