Heel spur and rest
Try to avoid putting strain on the foot as much as possible. Especially in the beginning stages of a heel spur or plantar fasciitis this is very important. Too much strain is one of the main factors contributing to a developing heelspur. Especially fanatic sporters should take it easy, which can be very hard ofcourse, but keep in mind that a heelspur can potentially put and end to your sport if you allow to let it become chronically.....
Dependant on how serious the injury is some light form of exercise may be beneficial, but is is best to discuss this with your doctor.
If you still want to keep sporting, you may switch to sports that do not put strain on your feet too much, like cycling or swimming. Still, beware on any strain: Cycling fanatically will put strain on the fascia again. Adjusting the pedals can be wise here.
Also persons with a profession that requires you to stand still on your feet a lot are vulnerable. Again here: try to avoid this, though your boss may not always agree....
Also overweight should be avoided, check the related article.
Don't walk on bare feet!
This is very stressfull for the heel spur. Even if you just need to walk a few meters to the toilet at night you should put on shoes or slippers, plus do a few stretches. Due to the feet being static for a few hours, these first few meters are very stressfull. Also check the article on stretching for this.