Wearing the wrong shoes can directly cause or contribute to plantar fasciitis and Achilles tendonitis. Especially shoes that are excessively worn https://drshoe.wordpress.com/2011/10/23/how-to-tell-when-your-athletic-shoes-are-worn-out/ or are the wrong size.
If you have already replaced your shoes, what else can you do? Achilles tendon stretches, that’s what. When the Achilles tendon is tight the foot compensates by pronating and pronation directly contributes to both Achilles tightness and plantar fasciitis.
Muscles attach tendons to bone and in this case, these two muscles join to form a common tendon, the Achilles. In this video, Whitney will show you how to stretch the Gastrocnemius and Soleus muscles. Performing these individual stretches daily in addition to wearing the right shoes, should get you back on track no time.
If the pain persists however, make an appointment with your nearest Sports Medicine Podiatrist for additional evaluation and treatment.
Dr. Jenny Sanders Shoe Blog 
Great information!
I had no idea that plantar faciitis and achilles tendonitist were related. I’ve also been told that rolling your foot on a tennis ball while seated is good for stretching the plantar facia. Is this a good idea, or is it doing damage? I’ve found it really relieves the pain for a while. Also I am wondering if shoes that are too loose or tight might be a factor.
I answered this question from Mark in following post https://drshoe.wordpress.com/2011/11/27/plantar-fasciitis-question/. Thanks Mark!