To avoid injury, it’s best to match the exercise routine to a specific goal. Then, make sure you are doing the exercise the right way and not too often. If you’re not sure about which type of exercise is right for you, your doctor can help you choose what’s best for your lifestyle and health.
If you do have an injury, like plantar fasciitis in your foot, the first step is good rehab. That could be as simple as putting a water bottle in the freezer, then rolling it on the foot to stretch out the plantar fascia. Hamstring stretches can help, as can stretching out the Achilles tendon, because it attaches to the heel, which goes to the plantar fascia.
The recommendation is about 150 minutes of moderate exercise a week. There is a limit, and once you go past that limit, you’re more prone to injuries. It all depends on level of activity and how you are progressing toward your goal. The idea is to be progressive, not aggressive. Let your body be your guide.