Start to Finish - Step One: Purchase the right shoe

1. Get EXPERT advice.   Buy your first pair of running shoes from a SPECIALTY RUNNING STORE.  Sure, you might be able to find cheaper shoes online, but you will need expert advice if it's your first pair of running shoes or if you haven't purchased a new pair in a while.  After you know exactly what works for you, you can do some bargain shopping the next time.
2. The SALESPERSON is your new buddy.  Plan on spending a bit of time at the running store.  If the salesperson is good as his or her job, you will be asked questions: what type of running you do, how often you run, where you typically run, if you're training for a race, and what type of surfaces you will be running on (asphalt, trail, sidewalk, track, treadmill).
3. YOUR FOOT.  The salesperson will look at the shape and arch of your foot to figure out what type of foot you have.  They will determine if you have flat, high-arched, or neutral feet.  This is important because it will help to narrow down what type of shoe you should try on.  
   
4. MEASURE YOUR FOOT.  The salesperson should measure your foot. My feet actually got smaller after I had children.  Also as you age your arch may fall causing a change in your shoe size.
5. GO A 1/2 TO A FULL SIZE BIGGER.  I always buy my running shoes a 1/2 size larger than my regular shoe size.  Your feet will swell when you run and you need plenty of room in the toebox. I still tend to end up with blisters and black toenails, especially when I do a lot of downhill running, but going up in size helps to minimize these problems.
6. GET A RUNNING ANALYSIS.  The salesperson will do a running analysis for you. Your foot strike will be recorded while you run, usually on on treadmill.  This will determine your running style: underpronate (foot rolls outward), overpronate (foot rolls inward) or supinate (foot rolls outward).  

7. THE SHOES.  Based on the shape of your feet and your running style, the salesperson will determine what type of shoe is best for your foot.  

8. 
   GO FOR A TEST DRIVE BEFORE YOU BUY.  Run in the running shoes that the salesperson recommends for you at the store. I usually forget to dress for a short run when I go and I regret it everytime.  I end up running in my levis, but I still do it. You won't be able to really know how they feel when you run unless you RUN in the shoes. You will need to test for fit, function, and comfort before making your final decision.
9. BREAK YOUR NEW SHOES IN.  Most running shoes will let return the shoes after 1-2 weeks. If not, buy them somewhere that will.  Return them if you develop blisters or foot pain after running in them for a few weeks.
10. 
    REPLACE YOUR SHOES AS RECOMMENDED.  Most running shoes only last about 300-500 miles, so keep track of your mileage and replace them as recommended.  If not, you may end up with feet or leg pain or other complications.