I've taught the following tips to many runners in my local Nashville area over the years. It works. I've used it myself for over 12 years.
A possible cause of plantar fasciitis is lack of support in the arch area. Sure, there are other causes, but stay with me on this one. Exercises, special socks, ice, and corticosteroids will help AFTER you get injured, but you want to prevent it from reoccurring. To do that, you must address the source… lack of support for your arch. Exercises will help with mild cases, but you should still give yourself more arch support.
Many running injuries start at the arch, not just plantar fasciitis. Try this. Stand barefoot. Step forward about a foot with your right foot, placing it very lightly on the ground. Then, shift your weight to right foot. Watch what happens. For many runners, the arch flattens. The ankle rocks slightly inward. The Achilles tendon bends to the inside. Finally, as you rock forward more, the shin rolls inward. Finally, the kneecap rolls inward. When you go for a long run, this twisting happens several thousand times. The end result can plantar fasciitis, Achilles tendonitis, ITB syndrome, chondromalacia. Repeat this test, but this time with your running shoes on. When you rock your weight forward, the ankle, Achilles, shin, and kneecap should stay in the proper plane. Since you are having plantar problems, you will probably still see some significant flexing.
I used to wear orthotics, but then I discovered that as the shoe aged or if I got a different model of shoe (or even the same model the next year) the orthotic would no longer fit. I decided to make my own. To begin, take out the existing insert. In most training shoes, it's a flimsy piece of cloth covered foam with only a tiny bit of extra support foam around the heel cup and under the arch. Since you have plantar fasciitis, you obviously need more support under the arch, but the reason shoe manufactures don't add more is that the insert would then be too much for runners with lower arches.
Try the easy fix first. Replace the original flimsy insert with an off-the-shelf orthotic, such as SuperFeet Green, SuperFeet Blue (less padding) or Powersteps. I've used all three. All are good and the fit is slightly different with each. Cost is about $30, except the SuperFeet Green is $35. I'd suggest you try them all to see if you can get a perfect fit right out of the box. Take your running shoes with you to try them on. Take out the existing insert, insert the new insert and stand up. If the fit is good, you should feel a little more pressure on the arch area of your foot than with the old insert. With the old insert, you probably felt nothing. Next, do the same exercise mentioned earlier. Step forward, put the right shoe down, and then put your weight on the shoe. The shoe should rock a little less to the inside than with the old insert. However, even with a good fit, it will still probably rock inwards somewhat. You don't want your shoe to fit like a brick. Next, try running with the shoe. Of course, by that time, you've been walking all day and the plantar fasciitis probably isn't bothering you, but if it is, you should notice a reduction of pain with the SuperFeet (PowerSteps) insert. Even with a perfect fit, you may still have some pain because you have already aggravated the plantar muscle. It will need to heal to eliminate all the pain.
In choosing the right insert for your current pair of shoes, be sure to try different sizes if your size is on the borderline between small and medium, or medium to large. The larger size may need to be trimmed, but it also has slightly more arch support. I prefer the slightly larger size and then trimming it, but that’s my arch, not yours. You be the judge.
Run in the shoe with the new insert. The pain should be less, but since the arch is already aggravated, it may take a few days to go away completely.
IMPORTANT. You MUST add some arch support to the shoes you wear when you are NOT running. You’ll be in these non-running shoes 14-16 hours a day. I found that a simple Dr Scholls leather arch support was enough for me. If you don't add support to your non-running shoes, you are just aggravating the arch with every non-running step.
WHEN OFF THE SHELF ORTHOTICS AREN’T ENOUGH
If the new insert doesn't solve the problem in a few days, or if you want to do what I do, follow the remaining steps. When I buy a new pair of shoes, I immediately take out the existing insert and start modifying it. You’ll need a pair of scissors, duct tape, and a few 12 inch squares of craft’s felt. It’s available at Wal Mart in the crafts section for 20 cents per one foot square. Buy several pieces. Cut this big piece into a few 2 inch squares. Remove the shoe insert. Add a few of these small squares of craft felt under your shoe’s insert in the arch area until you feel “support” on the arch when wearing the shoes. You’ll have to overlap the felt squares to avoid getting all the bulk in one place. Use a small strip of duct tape to hold the felt in place as you are testing the various felt positions. Put the insert back in the shoe. To test the fit, take your tape, felt squares, and scissors with you to a place where you can run at least 50 meters. Run out and see how it feels. Make a note of where you need to make adjustments. Jog back and adjust the felt by adding, moving or removing pieces as necessary. Repeat until it feels right. What’s “right?” you ask. Basically you want to feel support all along the arch, not just the front or the back or the outer edge. If you don’t feel noticeable support anywhere, just keep adding more felt until you do. You also don’t want to feel more support on the arch than anywhere else on the foot.
Next, take a longer run of a few miles by yourself. I’d strongly recommend that you wear a fanny belt and carry a pocket knife or blunt scissors (don't run with scissors!!!) , a few more squares of felt, and a small roll of tape. You’ll probably notice a need for some minor adjustment along the way. I carry an old almost empty roll of duct tape for this, but scotch tape will work for a couple of miles until you get back.
Getting this right will be trial and error for you at first. Basically, you keep adding felt along the inside of the arch area of the insert until you feel like you are running with a tennis ball under your arch. That’s too much, so you need to back off a bit. Of course, the 2 inch square is only a starting point, you can fold those felt squares or trim them to give you support in the area you need. Most likely, it will take 3-10 squares to build up the arch enough. The outside edge of the felt will stick out past the inside edge of the insert. How much it needs to stick out varies with different shoes. For me it’s typically a quarter inch to a full inch
IF THAT FAILS...
After your first real run, you’ll know if this is working for you. If it doesn’t work and the shoes aren’t worn out, repeat the process by adding felt to the arch of Powersteps or SuperFeet inserts. What works best for you won’t always be the same. In some of my running shoes, I use the existing insert and felt. In others, I use the PowerSteps. In others, only the SuperFeet insert works.
One caution. While this process will work on with stability, motion control, lightweight performance trainers, and some racing flats, it won’t work on some cushion shoes. These shoes as a rule are too unstable even with all the extra arch support.
This whole process may sound like a lot of work, but it’s a lot faster than making one trip to and from your doctor’s office. In fact, you’ll be able to complete the entire process faster than you can read these instructions once you’ve done it a couple of times. IF THAT FAILS, there are a couple more steps you can take, but this post is already too long. Try what's been suggested so far. It should be enough.